Light emitting device, method of manufacturing same and display device including same

ABSTRACT

A light emitting device includes: a first electrode and a second electrode facing each other, an emissive layer disposed between the first electrode and the second electrode and including a quantum dot, an electron auxiliary layer disposed between the emissive layer and the second electrode and including a plurality of nanoparticles, and a polymer layer between a portion of the second electrode and the electron auxiliary layer, wherein the nanoparticles include a metal oxide including zinc, wherein the second electrode has a first surface facing a surface of the electron auxiliary layer and a second surface opposite to the first surface, and the polymer layer is disposed on a portion of the second surface and a portion of the surface of the electron auxiliary layer, and wherein the polymer layer includes a polymerization product of a thiol compound and an unsaturated compound having at least two carbon-carbon unsaturated bonds.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional application of U.S. patent application Ser. No.16/530,253, filed on Aug. 2, 2019, which claims priority to and thebenefit of Korean Patent Application No. 10-2018-0090844, filed in theKorean Intellectual Property Office on Aug. 3, 2018, and all thebenefits accruing therefrom under 35 U.S.C. § 119, the contents of whichis incorporated herein by reference in its entirety.

BACKGROUND 1. Field

A light emitting device, a method of manufacturing the light emittingdevice, and a display device including the light emitting device aredisclosed.

2. Description of the Related Art

Light emitting devices including a semiconductor nanocrystal, also knownas a quantum dot (QD), have been developed. Unlike a bulk material, ananoparticle such as a quantum dot has intrinsic physicalcharacteristics (e.g., energy bandgap, melting point), which may bemodified by changing the particle size of the quantum dot. For example,when supplied with photoenergy or electrical energy, a quantum dot mayemit light in a wavelength corresponding to the particle size of thequantum dot. Accordingly, the quantum dot may be used in a lightemitting device emitting light of a particular wavelength.

An improved light emitting device including a quantum dot would bebeneficial.

SUMMARY

An embodiment provides a light emitting device having improvedperformance.

Another embodiment provides a display device including the lightemitting device.

Yet another embodiment provides a method of preparing the light emittingdevice.

A light emitting device according to an embodiment includes

a first electrode and a second electrode facing each other,

an emissive layer disposed between the first electrode and the secondelectrode and including a quantum dot, and

an electron auxiliary layer disposed between the emissive layer and thesecond electrode and including a plurality of nanoparticles,

wherein the nanoparticles includes a metal oxide including zinc,

wherein the second electrode has a first surface facing a surface of theelectron auxiliary layer and a second surface opposite to the firstsurface,

wherein the light emitting device further includes a polymer layerdisposed on at least a portion of the second surface and at least aportion of the surface of the electron auxiliary layer, and

wherein the polymer layer includes a polymerization product of a monomercombination including a thiol compound having at least one thiol groupand an unsaturated compound having at least two carbon-carbonunsaturated bonds.

The second electrode is disposed on a portion of the surface of theelectron auxiliary layer.

A work function of the first electrode may be higher than a workfunction of the second electrode.

The first electrode may include indium tin oxide.

The second electrode may include a conductive metal.

The quantum dot may not include cadmium.

The quantum dot may include indium and phosphorus.

The quantum dot may include a chalcogen element and zinc.

In the light emitting device, an absolute value of lowest unoccupiedmolecular orbital (LUMO) energy level of the quantum dot may be lessthan an absolute value of LUMO energy level of the metal oxide.

The metal oxide may have a composition represented by Chemical FormulaA:Zn_(1-x)M_(x)O  [Chemical Formula A]

wherein, M is Mg, Ca, Zr, W, Li, Ti, Y, Al, or a combination thereof and0≤x≤0.5.

The metal oxide may include a zinc oxide, a zinc magnesium oxide, or acombination thereof.

An average particle size of the plurality of nanoparticles may begreater than or equal to about 1 nanometer (nm) and/or less than orequal to about 10 nanometers.

The average particle size of the plurality of nanoparticles may begreater than or equal to about 1.5 nm and/or less than or equal to about5 nm.

The polymerization product may include a cross-linked polymer.

The polymer layer may be disposed directly on the at least portion ofthe second surface of the second electrode and directly on the at leastportion of the surface of the electron auxiliary layer.

The polymer layer may be in contact with the second surface of thesecond electrode and the electron auxiliary layer.

The polymer layer may cover the entire second surface of the secondelectrode.

The polymer layer may cover an entire area of an exposed surface of theelectron auxiliary layer.

The polymer layer covers an entire area of the second surface and anentire area of the surface of the electron auxiliary layer except forthe portion on which the second electrode is disposed.

The polymer layer may not include an unsaturated carboxylic acid, asaturated carboxylic acid, a polymer thereof, or a combination thereof.

The polymer layer may not include (meth)acrylic acid, benzoic acid,3-butenoic acid, crotonic acid, butyric acid, isobutyric acid, aceticacid, propionic acid, a polymer thereof, or a combination thereof

The electrode and the electron auxiliary layer, and optionally at leasta portion of the emissive layer may be integrated together by thepolymerization product.

The electron auxiliary layer may further includes an organic materialbetween the nanoparticles of the plurality of nanoparticles, and theorganic material may include the polymerization product, unreacted thiolcompound, unreacted unsaturated compound, or a combination thereof.

The electron auxiliary layer may include sulfur. The presence of sulfurmay be confirmed by, for example, a transmission electron microscopyenergy dispersive X-ray (TEM-EDX) profile.

In the electron auxiliary layer, a content of sulfur may be greater thanor equal to about 0.001 mole percent (mol %), or may be greater than orequal to about 0.01 mol %, relative to a total number of moles of zincin the electron auxiliary layer.

The electron auxiliary layer may further include a thiol moiety, asulfide moiety, or a combination thereof.

A content of carbon in the electron auxiliary layer may be greater thanor equal to about 4 wt %, based on a total weight of the electronauxiliary layer.

A content of carbon in the electron auxiliary layer may be greater thanor equal to about 5 wt %, based on a total weight of the electronauxiliary layer.

The electron auxiliary layer may have a content of carbon of greaterthan or equal to about 10 wt %, based on a total weight of the electronauxiliary layer.

The electron auxiliary layer may have a content of carbon of greaterthan or equal to about 15 wt %, based on a total weight of the electronauxiliary layer.

The electron auxiliary layer may have a content of carbon of greaterthan or equal to about 20 wt %, based on a total weight of the electronauxiliary layer.

The electron auxiliary layer may not include polyethyleneimine.

The thiol compound may include a center moiety and at least one HS—R—*group bound to the center moiety, wherein, R is a direct bond, asubstituted or unsubstituted C1 to C30 aliphatic hydrocarbon group(e.g., alkylene, alkenylene, alkynylene, or the like), a sulfonyl group,a carbonyl group, an ether group, a sulfide group, a sulfoxide group, anester group, an amide group, or a combination thereof, * is a portionbound to an adjacent atom of the center moiety, and the center moietymay include a carbon atom, a substituted or unsubstituted C1 to C30aliphatic hydrocarbon group, a substituted or unsubstituted C3 to C30alicyclic hydrocarbon group, a substituted or unsubstituted C6 to C30aromatic hydrocarbon group, a substituted or unsubstituted C3 to C30heteroarylene group, a substituted or unsubstituted C3 to C30heterocyclic group, or a combination thereof.

The monomer combination may include a multiple thiol compound having atleast two thiol groups, a monothiol compound having one thiol group, ora combination thereof.

The thiol compound may include a di(mercaptoacetate) compound, atri(mercaptoacetate) compound, a tetra(mercaptoacetate) compound, adi(mercaptopropionate) compound, a tri(mercaptopropionate) compound, atetra(mercaptopropionate) compound, an isocyanate compound including atleast two mercaptoalkyl carbonyloxyalkyl groups, an isocyanuratecompound including at least two mercaptoalkyl carbonyloxyalkyl groups,or a combination thereof.

The unsaturated compound may include a center moiety and at least twoX′—R—* groups bound to the center moiety, wherein, X′ is a moietyincluding a carbon-carbon unsaturated bond, R is a direct bond, asubstituted or unsubstituted C1 to C30 aliphatic hydrocarbon group(e.g., alkylene, alkenylene, alkynylene, or the like), a sulfonyl group,a carbonyl group, an ether group, a sulfide group, an sulfoxide group,an ester group, an amide group, or a combination thereof, and the centermoiety may include a carbon atom, a substituted or unsubstituted C1 toC30 aliphatic hydrocarbon group, a substituted or unsubstituted C3 toC30 alicyclic hydrocarbon group, a substituted or unsubstituted C6 toC30 aromatic hydrocarbon group, a substituted or unsubstituted C3 to C30heteroarylene group, a substituted or unsubstituted C3 to C30heterocyclic group, or a combination thereof.

The unsaturated compound may include a di(meth)acrylate compound, atri(meth)acrylate compound, a tetra(meth)acrylate compound, apenta(meth)acrylate compound, a hexa(meth)acrylate compound, or acombination thereof.

The unsaturated compound may not include a carboxylic acid group.

The monomer combination may further include a monounsaturated compoundhaving one carbon-carbon unsaturated bond at the terminal end, forexample, a monoacrylate compound having one (meth)acrylate group and nothaving other polymerizable moiety.

The monomer combination may include a monothiol compound together with amulti-thiol compound.

The polymerization product may include a triazine moiety, atriazinetrione moiety, a quinoline moiety, a quinolone moiety, or acombination thereof.

The emissive layer may further include an organic material between thequantum dots, and the organic materials may include the polymerizationproduct, unreacted thiol compound, unreacted unsaturated compound, or acombination thereof.

The light emitting device may further include a hole auxiliary layerdisposed between the first electrode and the emissive layer.

In another embodiment, a method of manufacturing the aforementionedlight emitting device includes

providing a stack structure including a first electrode and a secondelectrode facing each other, an emissive layer disposed between thefirst electrode and the second electrode and including a quantum dot,and an electron auxiliary layer disposed between the emissive layer andthe second electrode and including a plurality of nanoparticles, whereinthe plurality of nanoparticles includes a metal oxide including zinc,and the second electrode has a first surface facing the surface of theelectron auxiliary layer and a second surface opposite to the firstsurface;

providing a polymer precursor mixture (also referred to as a monomercombination or a monomer mixture) including a thiol compound having atleast one thiol (SH) group and an unsaturated compound having at leasttwo carbon-carbon unsaturated bonds;

applying the polymer precursor mixture on at least a portion of thesecond surface of the second electrode and on at least a portion of thesurface of the electron auxiliary layer to form a polymer precursorlayer; and

polymerizing the thiol compound and the unsaturated compound in thepolymer precursor layer to form the light emitting device.

The polymerizing of the monomer combination may be performed for lessthan about 4 hours. In the method, the polymer precursor mixturepenetrates and diffuses between nanoparticles of the plurality ofnanoparticles in the electron auxiliary layer before the polymerizing,during the polymerizing, or a combination thereof.

The method further includes allowing the stack structure on which thepolymer precursor layer is formed to stand for at least 1 minute betweenthe forming of the polymer precursor layer on the stack structure andthe polymerizing of the thiol compound and the unsaturated compound inthe polymer precursor layer.

The polymerization of the monomer combination in the polymer precursorlayer may be performed in an atmosphere without oxygen.

The method further includes allowing the stack structure on which thepolymer precursor layer is formed to stand for at least 5 minutesbetween the forming of the polymer precursor layer on the stackstructure and the polymerizing of the thiol compound and the unsaturatedcompound in the polymer precursor layer.

The polymerizing may be performed at a temperature of greater than orequal to about 30° C. and less than or equal to about 100° C.

The polymer precursor mixture may further include a photoinitiator andthe polymerizing of the polymer precursor layer may includephotopolymerization.

Another embodiment provides a display device including theaforementioned light emitting device.

In the embodiments, a quantum dot-based electroluminescent device havingan improved efficiency and a prolonged life-span is provided. Further,the quantum dots do not include cadmium. The device according to anembodiment may prevent/suppress the life-span deterioration caused bydetachment (or elimination) of a ligand from a surface of the quantumdots detachment, which may occur during operation of the light emittingdevice. Further, by employing the aforementioned electron auxiliarylayer including metal oxide nanoparticles, performance degradation ofthe light emitting device, caused by surface defects in thenanoparticles, may be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other advantages and features of this disclosure willbecome more apparent by describing in further detail exemplaryembodiments thereof with reference to the accompanying drawings, inwhich:

FIG. 1 is a schematic cross-sectional view of a light emitting deviceaccording to an embodiment;

FIGS. 2A-2D are schematic views showing a process of manufacturing alight emitting device according to an embodiment;

FIG. 3A is a graph of luminance (candelas per square meter, Cd/m²)versus voltage (volts, V), showing the electro-luminescence propertiesof the light emitting devices manufactured in Examples 1 and 2 andComparative Examples 1 and 3;

FIG. 3B is a graph of luminance (Cd/m²) versus voltage (V), showing theelectro-luminescence properties of the light emitting devicesmanufactured in Examples 3 and 4 and Comparative Example 2;

FIG. 4A is a graph of current density (milliamperes per squarecentimeter, mA/cm²) versus voltage (V), showing electro-luminescenceproperties of the light emitting devices manufactured in Examples 1 and2 and Comparative Examples 1 and 3;

FIG. 4B is a graph of current density (mA/cm²) versus voltage (V),showing electro-luminescence properties of the light emitting devicesmanufactured in Examples 3 and 4 and Comparative Example 2;

FIG. 5A is a graph of external quantum efficiency (EQE, percent (%))versus luminance (Cd/m²), showing electro-luminescence properties of thelight emitting devices manufactured in Examples 1 and 2 and ComparativeExamples 1 and 3;

FIG. 5B is a graph of external quantum efficiency (EQE, percent (%))versus luminance (Cd/m²), showing electro-luminescence properties of thelight emitting devices manufactured in Examples 3 and 4 and ComparativeExample 2;

FIG. 6 is graph of photoluminescence intensity (arbitrary units, a.u.)versus wavelength (nm), showing photoluminescence properties of Ref.structure and stack structure having a polymer layer of ExperimentalExample 2; and

FIG. 7 shows a transmission electron microscope image of a cross-sectionof the light emitting device manufactured in Example 1.

DETAILED DESCRIPTION

Hereinafter, example embodiments of the present disclosure will bedescribed in detail so that a person skilled in the art would understandthe same. This disclosure may, however, be embodied in many differentforms and is not construed as limited to the example embodiments setforth herein.

In the drawings, the thickness of layers, films, panels, regions, etc.,are exaggerated for clarity. Like reference numerals designate likeelements throughout the specification. It will be understood that whenan element such as a layer, film, region, or substrate is referred to asbeing “on” another element, it can be directly on the other element orintervening elements may also be present. In contrast, when an elementis referred to as being “directly on” another element, there are nointervening elements present.

It will be understood that, although the terms “first,” “second,”“third,” etc. may be used herein to describe various elements,components, regions, layers, and/or sections, these elements,components, regions, layers, and/or sections should not be limited bythese terms. These terms are only used to distinguish one element,component, region, layer, or section from another element, component,region, layer, or section. Thus, “a first element,” “component,”“region,” “layer,” or “section” discussed below could be termed a secondelement, component, region, layer, or section without departing from theteachings herein.

As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items. Expressions such as “atleast one of,” when preceding a list of elements, modify the entire listof elements and do not modify the individual elements of the list.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a,” “an,” and “the” are intended to include the pluralforms, including “at least one,” unless the content clearly indicatesotherwise. “At least one” is not to be construed as limiting “a” or“an.” “or” means “and/or.” As used herein, the term “and/or” includesany and all combinations of one or more of the associated listed items.It will be further understood that the terms “comprises” and/or“comprising,” or “includes” and/or “including” when used in thisspecification, specify the presence of stated features, regions,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components, and/orgroups thereof.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper,” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

“About” or “approximately” as used herein is inclusive of the statedvalue and means within an acceptable range of deviation for theparticular value as determined by one of ordinary skill in the art,considering the measurement in question and the error associated withmeasurement of the particular quantity (i.e., the limitations of themeasurement system). For example, “about” can mean within one or morestandard deviations, or within ±10% or 5% of the stated value.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

Hereinafter, a work function or an energy level (e.g., highest occupiedmolecular orbital (HOMO) or Lowest unoccupied molecular orbital (LUMO)is expressed as an absolute value relative to a vacuum. In addition,when the work function, or the energy level, is referred to as “deep,”“high” or “large,” the work function or the energy level has a largeabsolute value based on a vacuum, i.e., 0 eV, while when the workfunction or the HOMO energy level is referred to as “shallow,” “low,” or“small,” the work function or HOMO energy level has a small absolutevalue, based on a vacuum.

As used herein, the term “Group II” refers to Group IIA and Group IIB ofthe Periodic Table of the elements, and examples of Group II metals mayinclude Cd, Zn, Hg, and Mg, but are not limited thereto.

As used herein, the term “Group III” refers to Group IIIA and Group IIIBof the Periodic Table of the elements, and examples of Group III metalsmay include Al, In, Ga, and TI, but are not limited thereto.

As used herein, the term “Group IV” may refer to Group IVA and Group IVBof the Periodic Table of the elements, and examples of a Group IV metalmay include Si, Ge, and Sn, but are not limited thereto.

As used herein, the term “metal” refers to metallic or metalloidelements as defined in the Periodic Table of Elements selected fromGroups 1 to 17 of the Periodic Table of the elements, including thelanthanide elements and the actinide elements, and includes a semi-metalsuch as Si.

As used herein, the term “Group I” may refer to Group IA and Group IB ofthe Periodic Table of the elements, and examples may include Li, Na, K,Rb, and Cs, but are not limited thereto.

As used herein, the term “Group V” may refer to Group VA of the PeriodicTable of the elements, and examples may include nitrogen, phosphorus,arsenic, antimony, and bismuth, but are not limited thereto.

As used herein, the term “Group VI” may refer to Group VIA of thePeriodic Table of the elements, and examples may include sulfur,selenium, and tellurium, but are not limited thereto.

As used herein, unless a definition is otherwise provided, “substituted”refers to the replacement of hydrogen of a compound, a group, or amoiety by at least one (e.g., 1, 2, 3, or 4) substituent independentlyselected from a C1 to C30 alkyl group, a C2 to C30 alkenyl group, a C2to C30 alkynyl group, a C2 to C30 epoxy group, a C2 to C30 alkenylgroup, a C2 to C30 alkyl ester group, a C3 to C30 alkenyl ester group(e.g., acrylate group, methacrylate group), a C6 to C30 aryl group, a C7to C30 alkylaryl group, a C1 to C30 alkoxy group, a C1 to C30heteroalkyl group, a C3 to C30 heteroalkylaryl group, a C3 to C30cycloalkyl group, a C3 to C15 cycloalkenyl group, a C6 to C30cycloalkynyl group, a C2 to C30 heterocycloalkyl group, a halogen (—F,—Cl, —Br, or —I), a hydroxy group (—OH), a nitro group (—NO₂), a cyanogroup (—CN), an amino group (—NRR′ wherein R and R′ are independentlyhydrogen or a C1 to C6 alkyl group), an azido group (—N₃), an amidinogroup (—C(═NH)NH₂), a hydrazino group (—NHNH₂), a hydrazono group(═N(NH₂)), an aldehyde group (—C(═O)H), a carbamoyl group (—C(O)NH₂), athiol group (—SH), an ester group (—RC(═O)O, wherein R is a C1 to C6alkyl group or a C6 to C12 aryl group), a carboxyl group (—COOH) or asalt thereof (—O(═O)OM, wherein M is an organic or inorganic cation), asulfonic acid group (—SO₃H) or a salt thereof (—SO₃M, wherein M is anorganic or inorganic cation), a phosphoric acid group (—PO₃H₂) or a saltthereof (—PO₃MH or —PO₃M₂, wherein M is an organic or inorganic cation),and a combination thereof.

As used herein, “alkyl” means a straight or branched chain, saturated,monovalent hydrocarbon group (e.g., methyl or hexyl).

As used herein, “alkenyl” means a straight or branched chain, monovalenthydrocarbon group having at least one carbon-carbon double bond (e.g.,ethenyl (—HC═CH₂)).

As used herein “alkynyl” means a straight or branched chain, monovalenthydrocarbon group having at least one carbon-carbon triple bond (e.g.,ethynyl).

As used herein, “alkylene” means a straight or branched chain,saturated, aliphatic hydrocarbon group having a valence of at least two,(e.g., methylene (—CH₂—) or, propylene (—(CH₂)₃—)). “Alkenylene” means astraight or branched chain hydrocarbon group having at least onecarbon-carbon double bond and having a valence of at least two,optionally substituted with one or more substituents where indicated,provided that the valence of the alkyl group is not exceeded.

As used herein, “cycloalkylene” means a cyclic alkylene group having avalence of at least two.

As used herein, “arylene” means a radical having a valence of at leasttwo, formed by the removal of at least two hydrogen atoms from one ormore rings of an aromatic hydrocarbon, wherein the hydrogen atoms may beremoved from the same or different rings (preferably different rings),each of which rings may be aromatic or nonaromatic. “Heteroarylene”means a radical having a valence of at least two formed by the removalof at least two hydrogen atoms from one or more rings of a heteroarylmoiety, wherein the hydrogen atoms may be removed from the same ordifferent rings (preferably the same ring), each of which rings may bearomatic or nonaromatic.

A “chalcogen” is an element of Group 16, e.g., oxygen, sulfur, selenium,or tellurium.

As used herein, “a substituted or unsubstituted C2 to C30 aliphatichydrocarbon group in which at least one methylene is substituted by asulfonyl group, a carbonyl group, an ether group, a sulfide group, ansulfoxide group, an ester group, an amide group, or a combinationthereof” refers to a group obtained by replacing at least one methylenein a substituted or unsubstituted C2 to C30 aliphatic hydrocarbon groupby a sulfonyl group, a carbonyl group, an ether group, a sulfide group,an sulfoxide group, an ester group, an amide group, or a combinationthereof.

As used herein, a particle size or an average particle size may bemeasured by using an electron microscope analysis and optionally acommercially available image analysis program (e.g., Image J). Theaverage may be mean or median.

Hereinafter, a light emitting device according to an embodiment isdescribed with reference to drawings.

FIG. 1 is a schematic cross-sectional view of a light emitting deviceaccording to an embodiment.

Referring to FIG. 1, a light emitting device 10 according to anembodiment includes a first electrode 11 and a second electrode 15facing each other, an emissive layer 13 disposed between the firstelectrode 11 and the second electrode 15 and including a quantum dot, ahole auxiliary layer 12 disposed between the first electrode 11 and theemissive layer 13, and an electron auxiliary layer 14 disposed betweenthe second electrode 15 and the emissive layer 13.

A substrate (not shown) may be disposed at the side of the firstelectrode 11 or the second electrode 15. In an embodiment, the substratemay be disposed at the side of the first electrode. The substrate mayinclude an insulating material (e.g., insulating transparent substrate).The substrate may include glass; a polymer such as an ester (e.g.,polyethylene terephthalate (PET), polyethylene naphthalate (PEN)), apolycarbonate, a polyacrylate, a polyimide, a polyamideimide, apolysiloxane (e.g. PDMS), or a combination thereof; an inorganicmaterial such as Al₂O₃, ZnO, or a combination thereof; or a combinationcomprising a least two of the foregoing, but is not limited thereto. Thesubstrate may be made of a silicon wafer. As used herein, the term“transparent” refers to having a transmittance of greater than or equalto about 85% transmittance of light having a predetermined wavelength(e.g., light emitted from a quantum dot), or for example, transmittanceof greater than or equal to about 88%, greater than or equal to about90%, greater than or equal to about 95%, greater than or equal to about97%, or greater than or equal to about 99%, e.g., about 85% to about99.99%, or about 90% to about 99.9%. A thickness of the substrate may beappropriately selected considering a substrate material but is notparticularly limited. The transparent substrate may be flexible. Thesubstrate may be omitted.

The first electrode 11 may be an anode and the second electrode 15 maybe a cathode.

The first electrode 11 may be made of an electrically conductivematerial, for example a metal, a conductive metal oxide, or acombination thereof. The first electrode 11 may include, for example, ametal or an alloy thereof, the metal including nickel, platinum,vanadium, chromium, copper, zinc, and gold; a conductive metal oxidesuch as zinc oxide, indium oxide, tin oxide, indium tin oxide (ITO),indium zinc oxide (IZO), or fluorine doped tin oxide; or a combinationof metal and a metal oxide such as ZnO and Al or SnO₂ and Sb, but is notlimited thereto. A combination comprising at least one of the foregoingmay also be used. In an embodiment, the first electrode may include atransparent conductive metal oxide, for example, indium tin oxide. Awork function of the first electrode may be greater than a work functionof the second electrode. Alternatively, a work function of the firstelectrode may be less than a work function of the second electrode.

The second electrode 15 may be made of a conductive material, forexample a metal, a conductive metal oxide, a conductive polymer, or acombination thereof. The second electrode 15 may include, for example, ametal or an alloy thereof, such as aluminum, magnesium, calcium, sodium,potassium, titanium, indium, yttrium, lithium, gadolinium silver, gold,platinum, tin, lead, cesium, or barium; a multi-layer structuredmaterial such as LiF/Al, LiO₂/Al,8-hydroxyquinolinolato-lithium/aluminum (Liq/Al), LiF/Ca, or BaF₂/Ca,but is not limited thereto. A combination comprising at least two of theforegoing may also be used. The conductive metal oxide is the same asdescribed above.

In an embodiment, the work function of the first electrode 11 may be,for example, about 4.5 electron volts (eV) to about 5.0 eV and the workfunction of the second electrode 15 may be for example greater than orequal to about 4.0 eV and less than about 4.5 eV. Within these ranges,the work function of the first electrode 11 may be for example about 4.6eV to about 4.9 eV and the work function of the second electrode 15 maybe for example about 4.0 eV to about 4.3 eV.

At least one of the first electrode 11 and the second electrode 15 maybe a light-transmitting electrode and the light-transmitting electrodemay be for example made of a conductive oxide such as a zinc oxide, anindium oxide, a tin oxide, an indium tin oxide (ITO), an indium zincoxide (IZO), a fluorine doped tin oxide, a metal thin layer including asingle layer or a multilayer, or a combination thereof. When one of thefirst electrode 11 and the second electrode 15 is anon-light-transmitting (e.g., non-transparent) electrode, it mayinclude, for example, an opaque conductive material such as aluminum(Al), silver (Ag), gold (Au), or a combination thereof.

A thickness of the electrodes (the first electrode and/or the secondelectrode) is not particularly limited and may be appropriately selectedwith consideration of the device efficiency. For example, the thicknessof the electrodes may be greater than or equal to about 5 nanometers(nm), for example, greater than or equal to about 50 nm, or greater thanor equal to about 1 μm. For example, the thickness of the electrodes maybe less than or equal to about 100 micrometers (μm), for example, lessthan or equal to about 10 μm, less than or equal to about 1 μm, lessthan or equal to about 900 nm, less than or equal to about 500 nm, orless than or equal to about 100 nm.

The emissive layer 13 includes a quantum dot. The quantum dot(hereinafter, also referred to as a semiconductor nanocrystal) mayinclude a Group II-VI compound, a Group III-V compound, a Group IV-VIcompound, a Group IV element or compound, a Group compound, a Groupcompound, a Group I-II-IV-VI compound, or a combination thereof.

The quantum dot may not include cadmium. In an aspect, the quantum dotdoes not include cadmium. In an aspect, a content of cadmium in thequantum dot may be 0.1 weight percent (wt %) to 0.000001 wt %, or 0.01wt % to 0.0001 wt %, based on a total weight of the quantum dot.

The Group II-VI compound may include a binary element compound includingCdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, MgSe, MgS, or acombination thereof; a ternary element compound including CdSeS, CdSeTe,CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe,CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, MgZnSe, MgZnS, ora combination thereof; or a quaternary element compound includingHgZnTeS, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe,HgZnSeS, HgZnSeTe, HgZnSTe, or a combination thereof. The Group II-VIcompound may further include a Group III metal. A combination comprisingat least two of the foregoing may also be used.

The Group III-V compound may include a binary element compound includingGaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, or acombination thereof; a ternary element compound including GaNP, GaNAs,GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs,InNSb, InPAs, InZnP, InPSb, or a combination thereof; or a quaternaryelement compound including GaAlNP, GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb,GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb,InAlPAs, InAlPSb, InZnP, or a combination thereof. The Group III-Vcompound may further include a Group II metal (e.g., InZnP).

The Group IV-VI compound may include a binary element compound includingSnS, SnSe, SnTe, PbS, PbSe, PbTe, or a combination thereof; a ternaryelement compound including SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe,SnPbS, SnPbSe, SnPbTe, or a combination thereof; or a quaternary elementcompound including SnPbSSe, SnPbSeTe, SnPbSTe, or a combination thereof.

Examples of the Group compound may include CuInSe₂, CuInS₂, CuInGaSe, orCuInGaS, but are not limited thereto. Examples of the Group I-II-IV-VIcompound may include CuZnSnSe or CuZnSnS, but are not limited thereto.The Group IV element or compound may include a single substance selectedfrom Si, Ge, or a combination thereof; or a binary element compoundincluding SiC, SiGe, or a combination thereof. A combination comprisingat least two of the foregoing may also be used.

In an embodiment, the quantum dot may not include cadmium. The quantumdot may include a Group III-V compound-based semiconductor nanocrystalincluding indium and phosphorus. The Group III-V compound may furtherinclude zinc. The quantum dot may include a Group II-VI compound-basedsemiconductor nanocrystal including a chalcogen element (e.g., sulfur,selenium, tellurium, or a combination thereof) and zinc.

In the quantum dot, the aforementioned binary element compound, ternaryelement compound and/or the quaternary element compound, respectivelyexist in a uniform concentration in the semiconductor nanocrystalparticle or may be present in partially different concentrations in thesame particle. The semiconductor nanocrystals may have a core/shellstructure wherein a first semiconductor nanocrystal (shell) surrounds asecond semiconductor nanocrystal (core) having the same or differentcomposition. In an embodiment, the quantum dots may include a coreincluding InP, InZnP, ZnSe, ZnSeTe, or a combination thereof and a shell(single layer or a multi-layered shell) including ZnSe, ZnS, ZnSeS, or acombination thereof.

The core and the shell may have an interface, and an element of at leastone of the core or the shell in the interface may have a concentrationgradient, for example, the concentration of the element in the shelldecreases from an outer surface of the shell toward the core. Thesemiconductor nanocrystal may have a structure including onesemiconductor nanocrystal core and a multi-layer shell surrounding thesame. Herein, the term multi-layer shell refers to at least two shells(two layers) wherein each shell (layer) may be a single composition, analloy, and/or have a concentration gradient.

In the quantum dot, the material of the shell (i.e., the shell material)and the material of the core (i.e., the core material) may have adifferent bandgap energy than each other. For example, the bandgapenergy of the shell material may be greater than the bandgap energy ofthe core material. According to an aspect, the bandgap energy of theshell material may less than the bandgap energy of the core material.The quantum dot may have a multi-layer shell. In the multi-layer shell,the bandgap energy of the outer layer (i.e., the layer further away fromthe core) may be greater than the bandgap energy of the inner layer(i.e., the layer closer to the core). In the multi-layer shell, thebandgap energy of the outer layer may be less than the bandgap energy ofthe inner layer.

The absorption/photoluminescence wavelengths of the quantum dot may bemodified by selecting a composition and a size of the quantum dot. Amaximum photoluminescence peak wavelength of the quantum dot may bewithin an ultraviolet (UV) to infrared wavelength or may be a wavelengthgreater than the above wavelength range.

In an embodiment, the quantum dot may emit blue light. For example,maximum photoluminescence peak wavelength of the quantum dot may begreater than or equal to about 430 nm, for example, greater than orequal to about 440 nm, greater than or equal to about 450 nm, greaterthan or equal to about 451 nm, greater than or equal to about 452 nm,greater than or equal to about 453 nm, greater than or equal to about454 nm, greater than or equal to about 455 nm, greater than or equal toabout 456 nm, greater than or equal to about 457 nm, greater than orequal to about 458 nm, greater than or equal to about 459 nm, or greaterthan or equal to about 460 nm, and less than or equal to about 490 nm,for example, less than or equal to about 480 nm, less than or equal toabout 470 nm, less than or equal to about 468 nm, less than or equal toabout 467 nm, less than or equal to about 466 nm, or less than or equalto about 465 nm.

In an embodiment, the quantum dot may emit green light. The maximumphotoluminescence peak wavelength of the quantum dot may be greater thanor equal to about 490 nm, for example, greater than or equal to about500 nm, greater than or equal to about 510 nm, greater than or equal toabout 520 nm, or greater than or equal to about 530 nm, and less than orequal to about 560 nm, less than or equal to about 550 nm, less than orequal to about 545 nm, less than or equal to about 540 nm, or less thanor equal to about 535 nm.

In an embodiment, the quantum dot may emit red light. The maximumphotoluminescence peak wavelength of the quantum dot may be greater thanor equal to about 600 nm, for example, greater than or equal to about610 nm, greater than or equal to about 615 nm, or greater than or equalto about 620 nm and less than or equal to about 650 nm, less than orequal to about 645 nm, less than or equal to about 640 nm, less than orequal to about 635 nm, or less than or equal to about 630 nm.

The quantum dot may have quantum efficiency of greater than or equal toabout 10%, for example, greater than or equal to about 30%, greater thanor equal to about 50%, greater than or equal to about 60%, greater thanor equal to about 70%, greater than or equal to about 90%, or even about100%.

The quantum dot may have a relatively narrow spectrum. The quantum dotmay have, for example, a full width at half maximum (FWHM) of aphotoluminescence wavelength spectrum of less than or equal to about 50nm, for example, less than or equal to about 45 nm, less than or equalto about 40 nm, or less than or equal to about 30 nm.

The quantum dot(s) may have a particle size (or an average particlesize) of greater than or equal to about 1 nm and less than or equal toabout 100 nm. The particle size may refer to a diameter or an equivalentdiameter which is calculated under the assumption it has a sphericalshape based upon a 2D image obtained by (e.g., transmission) electronmicroscope analysis. The quantum dot(s) may have a particle size (or anaverage particle size) of about 1 nm to about 50 nm or about 1 nm toabout 20 nm, and may be, for example, greater than or equal to about 2nm, greater than or equal to about 3 nm, or greater than or equal toabout 4 nm and less than or equal to about 50 nm, less than or equal toabout 40 nm, less than or equal to about 30 nm, less than or equal toabout 20 nm, less than or equal to about 15 nm, or less than or equal toabout 10 nm. The shapes of the quantum dot(s) are not particularlylimited. For example, the quantum dot may having a shape which includesa sphere, a polyhedron, a pyramid, a multipod, a square, a rectangularparallelepiped, a nanotube, a nanorod, a nanowire, a nanosheet, or acombination thereof, but is not limited thereto.

The quantum dot may be commercially available or may be appropriatelysynthesized. When the quantum dot is synthesized as a colloidaldispersion, the particle size of the quantum dot may be relativelyfreely and uniformly controlled.

The quantum dot may include an organic ligand (e.g., a ligand having ahydrophobic moiety or a hydrophilic moiety) on a surface thereof. Theorganic ligand may be attached (e.g., bound) to a surface of the quantumdot. The organic ligand may include RCOOH, RNH₂, R₂NH, R₃N, —RSH, R₃PO,R₃P, ROH, RCOOR, RPO(OH)₂, RHPOOH, R₂POOH, or a combination thereof,wherein, R is independently a C3 to C40 substituted or unsubstitutedaliphatic hydrocarbon group, such as a C3 to C40 (e.g., C5 or greaterand C24 or less) substituted or unsubstituted alkyl, a C3 to C40substituted or unsubstituted alkenyl, a C6 to C40 (e.g., C6 or greaterand C20 or less) substituted or unsubstituted aromatic hydrocarbongroup, such as a substituted or unsubstituted C6 to C40 aryl group, or acombination thereof.

Examples of the organic ligand may include a thiol compound such asmethane thiol, ethane thiol, propane thiol, butane thiol, pentane thiol,hexane thiol, octane thiol, dodecane thiol, hexadecane thiol, octadecanethiol, or benzyl thiol; an amine compound such as methane amine, ethaneamine, propane amine, butane amine, pentyl amine, hexyl amine, octylamine, nonylamine, decylamine, dodecyl amine, hexadecyl amine, octadecylamine, dimethyl amine, diethyl amine, dipropyl amine, tributylamine, ortrioctylamine; a carboxylic acid compound such as methanoic acid,ethanoic acid, propanoic acid, butanoic acid, pentanoic acid, hexanoicacid, heptanoic acid, octanoic acid, dodecanoic acid, hexadecanoic acid,octadecanoic acid, oleic acid, or benzoic acid; a phosphine compoundsuch as methyl phosphine, ethyl phosphine, propyl phosphine, butylphosphine, pentyl phosphine, octylphosphine, dioctyl phosphine,tributylphosphine, or trioctylphosphine; an oxide of a phosphinecompound such methyl phosphine oxide, ethyl phosphine oxide, propylphosphine oxide, butyl phosphine oxide, pentyl phosphine oxide,tributylphosphine oxide, octyl phosphine oxide, dioctyl phosphine oxide,or trioctyl phosphine oxide; a diphenyl phosphine compound, a triphenylphosphine compound, or an oxide compound thereof; C5 to C20 alkylphosphinic acid such as hexylphosphinic acid, octylphosphinic acid,dodecanephosphinic acid, tetradecanephosphinic acid,hexadecanephosphinic acid, octadecanephosphinic acid; a C5 to C20 alkylphosphonic acid such as hexyl phosphonic acid, octyl phosphonic acid,dodecane phosphonic acid, tetradecane phosphonic acid, hexadecanephosphonic acid, octadecane phosphonic acid; but are not limitedthereto. A combination comprising at least one of the foregoing may alsobe used. The quantum dot may include a hydrophobic organic ligand eitheralone or in a combination comprising two or more hydrophobic ligands.The hydrophobic organic ligand may not include a photopolymerizablemoiety (e.g., acrylate group, methacrylate group, etc.).

In an embodiment, the emissive layer 13 may include a monolayercomprising a plurality of quantum dots. In another embodiment, theemissive layer 13 may include at least one monolayer comprising aplurality of quantum dots, for example, 2 or more layers, 3 or morelayers, or 4 or more layers, and 20 or less layers, or 10 or lesslayers, 9 or less layers, 8 or less layers, 7 or less layers, or 6 orless layers.

The emissive layer 13 may have a thickness of greater than or equal toabout 5 nm, for example, greater than or equal to about 10 nm, greaterthan or equal to about 20 nm, or greater than or equal to about 30 nmand less than or equal to about 200 nm, for example, less than or equalto about 150 nm, less than or equal to about 100 nm, less than or equalto about 90 nm, less than or equal to about 80 nm, less than or equal toabout 70 nm, less than or equal to about 60 nm, or less than or equal toabout 50 nm. The emissive layer 13 may have, for example, a thickness ofabout 10 nm to about 150 nm, for example about 10 nm to about 100 nm,for example about 10 nm to about 50 nm.

A HOMO energy level of the emissive layer 13 may be greater than orequal to about 5.1 eV, greater than or equal to about 5.2 eV, greaterthan or equal to about 5.3 eV, greater than or equal to about 5.4 eV,greater than or equal to about 5.6 eV, greater than or equal to about5.7 eV, greater than or equal to about 5.8 eV, greater than or equal toabout 5.9 eV, or greater than or equal to about 6.0 eV. The emissivelayer 13 may have a HOMO energy level of less than or equal to about 7.0eV, less than or equal to about 6.8 eV, less than or equal to about 6.7eV, less than or equal to about 6.5 eV, less than or equal to about 6.3eV, or than or equal to about 6.2 eV.

The emissive layer 13 may have, for example, a LUMO energy level of lessthan or equal to about 4 eV, less than or equal to about 3.9 eV, lessthan or equal to about 3.8 eV, less than or equal to about 3.7 eV, lessthan or equal to about 3.6 eV, less than or equal to about 3.5 eV, lessthan or equal to about 3.4 eV, less than or equal to about 3.3 eV, lessthan or equal to about 3.2 eV, or less than or equal to about 3.0 eV.The emissive layer 13 may have a LUMO energy level of greater than orequal to about 2 eV.

If desired, the light emitting device according to an embodiment mayfurther include a hole auxiliary layer. The hole auxiliary layer 12 isdisposed between the first electrode 11 and the emissive layer 13. Thehole auxiliary layer 12 may include a hole injection layer (HIL), a holetransport layer (HTL), and/or an electron blocking layer (EBL). The holeauxiliary layer 12 may be a single layer or a multi-layer structureincluding adjacent layers of different components.

The HOMO energy level of the hole auxiliary layer 12 may be matched withthe HOMO energy level of the emissive layer 13 in order to facilitate amobility of a hole transmitted from the hole auxiliary layer 12 to theemissive layer 13.

The HOMO energy level of the hole auxiliary layer 12 adjacent to theemissive layer is equivalent to the HOMO energy level of the emissivelayer 13, or may be less than the HOMO energy level of the emissivelayer 13 by a value within a range of less than or equal to about 1.0eV. In an embodiment the hole auxiliary layer may be a hole transportlayer and/or a hole injection layer.

The HOMO energy level of the hole auxiliary layer 12 may be, forexample, greater than or equal to about 5.0 eV, greater than or equal toabout 5.2 eV, greater than or equal to about 5.4 eV, greater than orequal to about 5.6 eV, or greater than or equal to about 5.8 eV. Forexample, the HOMO energy level of the hole auxiliary layer 12 may beabout 5.0 eV to about 7.0 eV, about 5.2 eV to 6.8 eV, about 5.4 eV toabout 6.8 eV, about 5.4 eV to about 6.7 eV, about 5.4 eV to about 6.5eV, about 5.4 eV to about 6.3 eV, about 5.4 eV to about 6.2 eV, about5.4 eV to about 6.1 eV, about 5.6 eV to about 7.0 eV, about 5.6 eV toabout 6.8 eV, about 5.6 eV to about 6.7 eV, about 5.6 eV to about 6.5eV, about 5.6 eV to about 6.3 eV, about 5.6 eV to about 6.2 eV, about5.6 eV to about 6.1 eV, about 5.8 eV to about 7.0 eV, about 5.8 eV toabout 6.8 eV, about 5.8 eV to about 6.7 eV, about 5.8 eV to about 6.5eV, about 5.8 eV to about 6.3 eV, about 5.8 eV to about 6.2 eV, or about5.8 eV to about 6.1 eV.

In an embodiment, the hole auxiliary layer 12 may include a holeinjection layer and a hole transport layer, where the hole injectionlayer is nearer to the first electrode 11 and the hole transport layernearer to the emissive layer 13. Herein, the HOMO energy level of thehole injection layer may be about 5.0 eV to about 5.3 eV and the HOMOenergy level of the hole transport layer may be about 5.2 eV to about5.5 eV.

A material included in the hole auxiliary layer 12 is not particularlylimited and may include, for example, poly(9,9-dioctyl-fluorene-co-N-(4-butylphenyl)-diphenylamine) (TFB), apoly(C6-C40)arylamine, poly(N-vinylcarbazole),poly(3,4-ethylenedioxythiophene (PEDOT),poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS),polyaniline, polypyrrole, N,N,N′,N′-tetrakis(4-methoxyphenyl)-benzidine(TPD), 4,4-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl (alpha-NPD),m-MTDATA (4,4′,4″-tris[phenyl(m-tolyl)amino]triphenylamine),4,4′,4″-tris(N-carbazolyl)-triphenylamine (TCTA),1,1-bis[(di-4-tolylamino)phenylcyclohexane (TAPC), a p-type metal oxide(e.g., NiO, WO₃, MoO₃, etc.), a carbon-based material such as grapheneoxide, or a combination thereof, but is not limited thereto.

In the hole auxiliary layer including one or more of the hole injectionlayer, the hole transport layer, and the electron blocking layer, athickness of each of the hole injection layer, the hole transport layer,and the electron blocking layer may be independently selected. Forexample, the thickness of each layer may be greater than or equal toabout 5 nm, greater than or equal to about 10 nm, greater than or equalto about 15 nm, or greater than or equal to about 20 nm and less than orequal to about 50 nm, for example, less than or equal to about 40 nm,less than or equal to about 35 nm, or less than or equal to about 30 nm,but is not limited thereto.

The electron auxiliary layer 14 is disposed between the emissive layer13 and the second electrode 15. The electron auxiliary layer 14 mayinclude, for example, an electron injection layer (EIL), an electrontransport layer (ETL), a hole blocking layer (HBL), or a combinationthereof.

The electron auxiliary layer 14 may be an electron transport layer.

The electron auxiliary layer 14 includes a plurality of nanoparticles.The nanoparticles include a metal oxide including zinc.

The metal oxide may include a compound represented by Chemical FormulaA:Zn_(1-x)M_(x)O  Chemical Formula A

wherein, M is Mg, Ca, Zr, W, Li, Ti, Y, Al, or a combination thereof,and 0≤x≤0.5. In an embodiment, in Chemical Formula A, M may be magnesium(Mg). In an embodiment, in Chemical Formula A, x may be greater than orequal to about 0.01 and less than or equal to about 0.3, for example,less than or equal to about 0.25, less than or equal to about 0.2, orless than or equal to about 0.15.

The metal oxide may include a zinc oxide, a zinc magnesium oxide, or acombination thereof. The absolute value of LUMO energy level of aquantum dot included in the emissive layer may be less than the absolutevalue of LUMO energy level of the metal oxide. According to anotherembodiment, the LUMO energy level absolute value of the quantum dot maybe greater than the LUMO absolute value of the metal oxide ETL. Theabsolute value of LUMO energy level of a blue QD may be less than theabsolute value of LUMO energy level of the metal oxide ETL. The electroninjection which occurs in the electroluminescent device including a blueQD may be different from electron injection which occurs in a lightemitting device including a red or a green quantum dot.

An average particle size of the nanoparticles may be greater than orequal to about 1 nm, for example, greater than or equal to about 1.5 nm,greater than or equal to about 2 nm, greater than or equal to about 2.5nm, or greater than or equal to about 3 nm and less than or equal toabout 10 nm, less than or equal to about 9 nm, less than or equal toabout 8 nm, less than or equal to about 7 nm, less than or equal toabout 6 nm, or less than or equal to about 5 nm. The nanoparticles mayhave a spherical shape. The nanoparticles may not have a rod shape. Thenanoparticles may not have a nanowire shape.

In an embodiment, the electron auxiliary layer 14 may, include one ormore of an electron injection layer, an electron transport layer, or ahole blocking layer. A thickness of each of the electron injectionlayer, the electron transport layer, and the hole blocking layer may begreater than or equal to about 5 nm, greater than or equal to about 6nm, greater than or equal to about 7 nm, greater than or equal to about8 nm, greater than or equal to about 9 nm, greater than or equal toabout 10 nm, greater than or equal to about 11 nm, greater than or equalto about 12 nm, greater than or equal to about 13 nm, greater than orequal to about 14 nm, greater than or equal to about 15 nm, greater thanor equal to about 16 nm, greater than or equal to about 17 nm, greaterthan or equal to about 18 nm, greater than or equal to about 19 nm, orgreater than or equal to about 20 nm and less than or equal to about 120nm, less than or equal to about 110 nm, less than or equal to about 100nm, less than or equal to about 90 nm, less than or equal to about 80nm, less than or equal to about 70 nm, less than or equal to about 60nm, less than or equal to about 50 nm, less than or equal to about 40nm, less than or equal to about 30 nm, or less than or equal to about 25nm, but is not limited thereto.

In a device according to an embodiment, a second electrode 15 (acathode) is disposed on a portion of the surface 14 a of the electronauxiliary layer 14. The second electrode 15 does not cover the entiresurface of the electron auxiliary layer 14. The second electrode 15 hasa first surface 15 a facing the surface 14 a of the electron auxiliarylayer 14 and a second surface 15 b opposite to the first surface 15 a.

The light emitting device according to an embodiment includes a polymerlayer 16 disposed on (e.g., directly on) at least a portion of thesecond surface 15 b of the second electrode 15 and disposed on (e.g.directly on) at least a portion of the surface 14 a of the electronauxiliary layer 14. The polymer layer 16 may disposed on and cover theentire area of the surface 14 a of the electron auxiliary layer 14, andmay be disposed on and cover the entire area of the second surface 15 bof the second electrode 15. In an embodiment, the polymer layer 16 maybe disposed on the entire area of the second surface 15 b of the secondelectrode 15. The polymer layer 16 includes a polymer which is apolymerization product of a monomer combination including a thiolcompound having at least one thiol group and an unsaturated compoundhaving at least two carbon-carbon unsaturated bonds. The thiol compoundmay include a multiple thiol compound having at least two thiol groups,a monothiol compound having one thiol group, or a combination thereof.

The polymer layer may be disposed directly on (e.g., in contact with) atleast one portion of the second surface of the second electrode and atleast one portion of the surface of the electron auxiliary layer. Thepolymer layer may cover the entire portion (e.g., the entire area) ofthe second surface of the second electrode and may cover the entireportion of the surface of the electron auxiliary layer except for theportion on which the second electrode is disposed. The polymer layer mayhave, for example, a degree of polymerization (e.g., a curing degree) asconfirmed by infrared spectroscopic analysis, of greater than or equalto about 95%, for example, greater than or equal to about 96%, greaterthan or equal to about 97%, greater than or equal to about 98%, orgreater than or equal to about 99%.

The monomer combination including a thiol compound may include amultiple thiol compound and the multiple thiol compound may berepresented by Chemical Formula 1:

wherein, in Chemical Formula 1, R¹ is hydrogen, a substituted orunsubstituted C1 to C30 linear or branched alkyl group, a substituted orunsubstituted C6 to C30 aryl group, a substituted or unsubstituted C7 toC30 arylalkyl group, a substituted or unsubstituted C3 to C30 heteroarylgroup, a substituted or unsubstituted C3 to C30 cycloalkyl group, asubstituted or unsubstituted C3 to C30 heterocycloalkyl group, a C1 toC10 alkoxy group, a hydroxy group, —NH₂, a substituted or unsubstitutedC1 to C30 amine group (—NRR′, wherein R and R′ are independentlyhydrogen or a C1 to C30 linear or branched alkyl group, and are notsimultaneously hydrogen), an isocyanate group, a halogen, —ROR′ (whereinR is a substituted or unsubstituted C1 to C20 alkylene group and R′ ishydrogen or a C1 to C20 linear or branched alkyl group), an acyl halidegroup (—RC(═O)X, wherein R is a substituted or unsubstituted C1 to C20alkylene group and X is a halogen), —C(═O)OR′ (wherein R′ is hydrogen ora C1 to C20 linear or branched alkyl group), —CN, —C(═O)NRR′ or—C(═O)ONRR′ (wherein R and R′ are independently hydrogen or a C1 to C20linear or branched alkyl group), or a combination thereof,

L₁ is a carbon atom, a substituted or unsubstituted C1 to C30 alkylenegroup, a substituted or unsubstituted C2 to C30 alkenylene group, asubstituted or unsubstituted C3 to C30 cycloalkylene group, asubstituted or unsubstituted C6 to C30 arylene group, a substituted orunsubstituted C3 to C30 heteroarylene group (e.g., quinoline, quinolone,triazine, triazinetrione moiety, etc.), a C3 to C30 heterocycloalkylenegroup, or a substituted or unsubstituted C2 to C30 alkylene group or asubstituted or unsubstituted C3 to C30 alkenylene group where at leastone methylene (—CH₂—) is replaced by a sulfonyl group (—SO₂—), acarbonyl group ((—C(═O)), an ether group (—O—), a sulfide (—S—), asulfoxide group (—SO—), an ester group (—C(═O)O—), an amide group(—C(═O)NR—, wherein R is hydrogen or a C1 to C10 alkyl group), or acombination thereof,

Y₁ is a single bond, a substituted or unsubstituted C1 to C30 alkylenegroup, a substituted or unsubstituted C2 to C30 alkenylene group, or asubstituted C2 to C30 alkylene group or a substituted or unsubstitutedC3 to C30 alkenylene group where at least one methylene (—CH₂—) isreplaced by a sulfonyl group (—S(═O)₂—), a carbonyl group (—C(═O)—), anether group (—O—), a sulfide group (—S—), a sulfoxide group (—S(═O)—),an ester group (—C(═O)O—), an amide group (—C(═O)NR—, wherein R ishydrogen or a C1 to C10 linear or branched alkyl group), an imine group(—NR—, wherein R is hydrogen or a C1 to C10 linear or branched alkylgroup), or a combination thereof,

m is an integer of 1 or greater, for example 1 to 10,

k1 is 0 or an integer of 1 or greater, for example 1 to 10,

k2 is an integer of 1 or greater, for example 1 to 10, and

the sum of m and k2 is an integer of 3 or greater, for example 3 to 20,

provided that when Y₁ is not a single bond, m does not exceed thevalence of Y₁, and the sum of k1 and k2 does not exceed the valence ofLi.

The thiol compound (e.g., monothiol compound or the multiple thiolcompound) may include a center moiety and at least one HS—R—* groupbound to the center moiety (wherein, R is a direct bond, a substitutedor unsubstituted C1 to C30 aliphatic hydrocarbon group, a sulfonylgroup, a carbonyl group, an ether group, a sulfide group, a sulfoxidegroup, an ester group, an amide group, or a combination thereof, and *represents a point of attachment), and the center moiety is a carbonatom, a substituted or unsubstituted C1 to C30 aliphatic hydrocarbongroup, a substituted or unsubstituted C3 to C30 alicyclic hydrocarbongroup (e.g., tricycloalkane such as tricyclodecane), a substituted orunsubstituted C6 to C30 aromatic hydrocarbon group, a substituted orunsubstituted C3 to C30 heteroarylene group, a substituted orunsubstituted C3 to C30 heterocyclic group, or a combination thereof.

In the HS—R—* group bound to the center moiety, the R may be asubstituted C2 to C30 aliphatic hydrocarbon group where at least onemethylene is replaced by a sulfonyl group, a carbonyl group, an ethergroup, a sulfide group, a sulfoxide group, an ester group, an amidegroup, or a combination thereof.

The multiple thiol compound may be represented by Chemical Formula 1-1:

wherein, in Chemical Formula 1-1,

L₁′ is the same as L₁ of Chemical Formula 1, and may be for example,carbon, a substituted or unsubstituted C6 to C30 arylene group, asubstituted or unsubstituted C3 to C30 heteroarylene group, asubstituted or unsubstituted C3 to C30 cycloalkylene group, or asubstituted or unsubstituted C3 to C30 heterocycloalkylene group,

Y_(a) to Y_(d) are independently a single bond, a substituted orunsubstituted C1 to C30 alkylene group, a substituted or unsubstitutedC2 to C30 alkenylene group, or a substituted or unsubstituted C2 to C30alkylene group or a substituted or unsubstituted C3 to C30 alkenylenegroup where at least one methylene (—CH₂—) is replaced by a sulfonylgroup (—S(═O)₂—), a carbonyl group (—C(═O)—), an ether group (—O—), asulfide group (—S—), a sulfoxide group (—S(═O)—), an ester group(—C(═O)O—), an amide group (—C(═O)NR—) (wherein R is hydrogen or a C1 toC10 linear or branched alkyl group), an imine group (—NR—) (wherein R ishydrogen or a C1 to C10 linear or branched alkyl group), or acombination thereof, and

R_(a) to R_(d) are independently R¹ of Chemical Formula 1 or SH,provided that at least two of R_(a) to R_(d) are SH.

The center moiety, e.g., L₁ or L₁′ of Chemical Formula 1 or ChemicalFormula 1-1, may include a triazine moiety, a triazinetrione moiety, aquinoline moiety, a quinolone moiety, a naphthalene moiety, or acombination thereof.

The multiple thiol compound of Chemical Formula 1 may includenonanedithiol, glycol dimercaptopropionate (e.g., ethylene glycoldimercaptopropionate), trimethylolpropane tris(3-mercaptopropionate)having the structure of Chemical Formula 1-2, pentaerythritoltetrakis(3-mercaptopropionate) having the structure of Chemical Formula1-3, pentaerythritol tetrakis(2-mercaptoacetate) having the structure ofChemical Formula 1-4, tris[2-(3-mercaptopropionyloxy)alkyl] isocyanuratehaving the structure of Chemical Formula 1-5, a compound having thestructure of Chemical Formula 1-6, a compound having the structure ofChemical Formula 1-7, a compound having the structure of ChemicalFormula 1-8, or a combination thereof:

wherein, in Chemical Formula 1-5, R is a substituted or unsubstituted C1to C10 alkylene;

wherein, n is an integer of 1 to 20,

wherein, n is an integer of 1 to 20,

wherein, n is an integer of 1 to 20.

The multiple thiol compound may include a dimercaptoacetate compound, atrimercaptoacetate compound, a tetramercaptoacetate compound, adimercaptopropionate compound, a trimercaptopropionate compound, atetramercaptopropionate compound, an isocyanate compound including atleast two mercaptoalkylcarbonyloxyalkyl groups, an isocyanurate compoundincluding at least two mercaptoalkyl carbonyloxyalkyl groups, or acombination thereof.

The unsaturated compound may be represented by Chemical Formula 2:

wherein, X is a C2-C30 aliphatic organic group having a carbon-carbondouble bond or a carbon-carbon triple bond, a C6-C30 aromatic organicgroup having a carbon-carbon double bond or a carbon-carbon triple bond,or a C3-C30 alicyclic organic group having a carbon-carbon double bondor a carbon-carbon triple bond,

R² is hydrogen, a substituted or unsubstituted C1 to C30 linear orbranched alkyl group, a substituted or unsubstituted C6 to C30 arylgroup, a substituted or unsubstituted C3 to C30 heteroaryl group, asubstituted or unsubstituted C3 to C30 cycloalkyl group, a substitutedor unsubstituted C3 to C30 heterocycloalkyl group, a C1 to C10 alkoxygroup; a hydroxy group, —NH₂, a substituted or unsubstituted C1 to C30amine group (—NRR′, wherein R and R′ are independently hydrogen or a C1to C30 linear or branched alkyl group), an isocyanate group, a halogen,—ROR′ (wherein R is a substituted or unsubstituted C1 to C20 alkylenegroup R′ is hydrogen or a C1 to C20 linear or branched alkyl group), anacyl halide group (—RC(═O)X, wherein R is a substituted or unsubstitutedalkylene group and X is a halogen), —C(═O)OR′ (wherein R′ is hydrogen ora C1 to C20 linear or branched alkyl group), —CN, or —C(═O)ONRR′(wherein R and R′ are independently hydrogen or a C1 to C20 linear orbranched alkyl group),

L₂ is a carbon atom, a substituted or unsubstituted C1 to C30 alkylenegroup, a substituted or unsubstituted C2 to C30 alkenylene group, asubstituted or unsubstituted C3 to C30 cycloalkylene group, asubstituted or unsubstituted C6 to C30 arylene group, or a substitutedor unsubstituted C3 to C30 heteroarylene group (e.g., quinoline,quinolone, triazine, triazinetrione moiety, etc.), a C3 to C30heterocycloalkylene group, or a substituted or unsubstituted C2 to C30alkylene group or a substituted or unsubstituted C3 to C30 alkenylenegroup where at least one methylene (—CH₂—) is replaced by a sulfonylgroup (—SO₂—), a carbonyl group ((—C(═O)—), an ether group (—O—), asulfide group (—S—), a sulfoxide group (—SO—), an ester group(—C(═O)O—), an amide group (—C(═O)NR—) (wherein R is hydrogen or a C1 toC10 alkyl group), or a combination thereof,

Y₂ is a single bond, a substituted or unsubstituted C1 to C30 alkylenegroup, a substituted or unsubstituted C2 to C30 alkenylene group, or asubstituted or unsubstituted C2 to C30 alkylene group or a substitutedor unsubstituted C3 to C30 alkenylene group where at least one methylene(—CH₂—) is replaced by a sulfonyl group (—S(═O)₂—), a carbonyl group(—C(═O)—), an ether group (—O—), a sulfide group (—S—), a sulfoxidegroup (—S(═O)—), an ester group (—C(═O)O—), an amide group (—C(═O)NR—)(wherein R is hydrogen or a C1 to C10 linear or branched alkyl group),an imine group (—NR—) (wherein R is hydrogen or a C1 to C10 linear orbranched alkyl group), or a combination thereof,

n is an integer of 1 or greater, for example, 1 to 10,

k3 is 0 or an integer of 1 or greater, for example, 1 to 10,

k4 is an integer of 1 or greater, for example, 1 to 10,

the sum of n and k4 is an integer of 3 or more, for example 3 to 20, ndoes not exceed the valence of Y₂, and the sum of k3 and k4 does notexceed the valence of L₂.

In Chemical Formula 2, X may be an acrylate group, a methacrylate group,a C2 to C30 alkenyl group, a C2 to C30 alkynyl group, a substituted orunsubstituted C3 to C30 alicyclic organic group having a carbon-carbondouble bond or a carbon-carbon triple bond in the ring, a substituted orunsubstituted C3 to C30 heterocycloalkyl group having a carbon-carbondouble bond or a carbon-carbon triple bond in the ring, a C3 to C30alicyclic organic group substituted with a C2 to C30 alkenyl group or aC2 to C30 alkynyl group, or a C3 to C30 heterocycloalkyl groupsubstituted with a C2 to C30 alkenyl group or a C2 to C30 alkynyl group.

The unsaturated compound may include a center moiety and at least twoX′—R—* groups bound to the center moiety, wherein, X is a moietyincluding a carbon-carbon unsaturated bond, for example, X as defined inChemical Formula 2, R is direct bond, a substituted or unsubstituted C1to C30 aliphatic hydrocarbon group, where at least one methylene isreplaced by sulfonyl moiety, carbonyl moiety, ether moiety, sulfidemoiety, sulfoxide moiety, ester moiety, amide moiety, or a combinationthereof, and * indicates a point of attachment to the center moiety. Thecenter moiety may include a carbon atom, a substituted or unsubstitutedC1 to C30 aliphatic hydrocarbon group, a substituted or unsubstituted C3to C30 alicyclic hydrocarbon group, a substituted or unsubstituted C6 toC30 aromatic hydrocarbon group, a substituted or unsubstituted C3 to C30heteroarylene group, a substituted or unsubstituted C3 to C30heterocyclic group, or a combination thereof.

In the X′—R—*, R may be a substituted or unsubstituted C2 to C30aliphatic hydrocarbon group where at least one methylene is replaced bysulfonyl moiety, carbonyl moiety, ether moiety, sulfide moiety,sulfoxide moiety, ester moiety, amide moiety, or a combination thereof.

In the center moiety or Chemical Formula 2, L₂ may be a triazine moiety,a triazinetrione moiety, a quinoline moiety, a quinolone moiety, anaphthalene moiety, or a combination thereof.

The substituted or unsubstituted C3 to C30 alicyclic organic grouphaving the carbon-carbon double bond or the carbon-carbon triple bond inthe ring may include a norbornene group, a maleimide group, a nadimidegroup, a tetrahydrophthalimide group, or a combination thereof.

In Chemical Formula 2, L₂ may be a group including a pyrrolidine moiety,a tetrahydrofuran moiety, a pyridinemoiety, a pyrimidine moiety, apiperidine moiety, a triazine moiety, a triazinetrione moiety, atricycloalkane moiety (e.g. tricyclodecane), a tricycloalkene moiety, oran isocyanurate moiety.

The unsaturated compound may be a C4 to C100 diallyl compound, a C4 toC100 triallyl compound, a C4 to C100 diallylether compound, a C4 to C100triallylether compound, a C4 to C100 di(meth)acrylate compound, a C4 toC100 tri(meth)acrylate compound, a divinyl ether compound, or acombination thereof.

The unsaturated compound of Chemical Formula 2 may be a compoundrepresented by Chemical Formula 2-1, Chemical Formula 2-2, or ChemicalFormula 2-3.

In Chemical Formulae 2-1 and 2-2, Z₁ to Z₃ are independently a*—Y₂—X_(n) group, which is the same as defined for Chemical Formula 2;

wherein, in Chemical Formula 2-3,

L₂′ is carbon, a substituted or unsubstituted C1 to C30 alkylene group,a substituted or unsubstituted C2 to C30 alkenylene group, a substitutedor unsubstituted C2 to C30 alkylene group wherein at least one methylene(—CH₂—) is replaced by a sulfonyl group (—S(═O)₂—), a carbonyl group(—C(═O)—), an ether group (—O—), a sulfide group (—S—), a sulfoxidegroup (—S(═O)—), an ester group (—C(═O)O—), an amide group (—C(═O)NR—,wherein R is hydrogen or a C1 to C10 linear or branched alkyl group), animine group (—NR—, wherein R is hydrogen or a C1 to C10 linear orbranched alkyl group), a C6 to C10 cycloalkylene group, or a combinationthereof; a substituted or unsubstituted C3 to C30 alkenylene groupwherein at least one methylene (—CH₂—) is replaced by a sulfonyl group(—S(═O)₂—), a carbonyl group (—C(═O)—), an ether group (—O—), a sulfidegroup (—S—), a sulfoxide group (—S(═O)—), an ester group (—C(═O)O—), anamide group (—C(═O)NR—, wherein R is hydrogen or a C1 to C10 linear orbranched alkyl group), an imine group (—NR—, wherein R is hydrogen or aC1 to C10 linear or branched alkyl group), a C6 to C10 cycloalkylenegroup, or a combination thereof, a substituted or unsubstituted C6 toC30 arylene group, a substituted or unsubstituted C3 to C30heteroarylene group, a substituted or unsubstituted C3 to C30cycloalkylene group, or a substituted or unsubstituted C3 to C30heterocycloalkylene group,

Y_(a) to Y_(d) are independently a single bond, a substituted orunsubstituted C1 to C30 alkylene group, a substituted or unsubstitutedC2 to C30 alkenylene group, or a substituted or unsubstituted C2 to C30alkylene group or a substituted or unsubstituted C3 to C30 alkenylenegroup wherein at least one methylene (—CH₂—) is replaced by a sulfonylgroup (—S(═O)₂—), a carbonyl group (—C(═O)—), an ether group (—O—), asulfide group (—S—), a sulfoxide group (—S(═O)—), an ester group(—C(═O)O—), an amide group (—C(═O)NR—, wherein R is hydrogen or a C1 toC10 linear or branched alkyl group), an imine group (—NR—, wherein R ishydrogen or a C1 to C10 linear or branched alkyl group), or acombination thereof, and

R′_(a) to R′_(d) are independently R² or X as defined in ChemicalFormula 2, provided that at least two of R′_(a) to R′d are X as definedin Chemical Formula 2.

The unsaturated compound may include a compound of Chemical Formula 2-4,a compound of Chemical Formula 2-5, a compound of Chemical Formula 2-6,a compound of Chemical Formula 2-7, a compound of Chemical Formula 2-8,a compound of Chemical Formula 2-9, a compound of Chemical Formula 2-10,a compound of Chemical Formula 2-11, a compound of Chemical Formula2-12, a compound of Chemical Formula 2-13, a compound of ChemicalFormula 2-14, a compound of Chemical Formula 2-15, or a combinationthereof:

wherein, in Chemical Formula 2-7, R₁ is a C1 to C20 alkylene group, or aC2 to C20 alkylene group wherein at least one methylene (—CH₂—) isreplaced by a sulfonyl group (—S(═O)₂—), a carbonyl group (—C(═O)—), anether group (—O—), a sulfide group (—S—), a sulfoxide group (—S(═O)—),an ester group (—C(═O)O—), an amide group (—C(═O)NR—, wherein R ishydrogen or a C1 to C10 linear or branched alkyl group), an imine group(—NR—, wherein R is hydrogen or a C1 to C10 linear or branched alkylgroup), or a combination thereof, and R₂ is hydrogen or a methyl group;

wherein, in Chemical Formula 2-8, R is a C1 to C10 alkyl group;

wherein, in Chemical Formula 2-9, A is hydrogen, a C1 to C10 alkylgroup, or a hydroxy group, R₁ is a direct bond (single bond), a C1 toC20 alkylene group, or a C2 to C20 alkylene wherein at least onemethylene (—CH₂—) is replaced by a sulfonyl group (—S(═O)₂—), a carbonylgroup (—C(═O)—), an ether group (—O—), a sulfide group (—S—), asulfoxide group (—S(═O)—), an ester group (—C(═O)O—), an amide group(—C(═O)NR—, wherein R is hydrogen or a C1 to C10 linear or branchedalkyl group), an imine group (—NR—, wherein R is hydrogen or a C1 to C10linear or branched alkyl group), or a combination thereof, and R₂ ishydrogen or a methyl group;

wherein, in Chemical Formula 2-10, R₁ is a single bond, a C1 to C20alkylene, or a C1 to C20 alkylene wherein at least one methylene (—CH₂—)is replaced by a sulfonyl group (—S(═O)₂—), a carbonyl group (—C(═O)—),an ether group (—O—), a sulfide group (—S—), a sulfoxide group(—S(═O)—), an ester group (—C(═O)O—), an amide group (—C(═O)NR—, whereinR is hydrogen or a C1 to C10 linear or branched alkyl group), an iminegroup (—NR—, wherein R is hydrogen or a C1 to C10 linear or branchedalkyl group), or a combination thereof, and R₂ is hydrogen or a methylgroup;

wherein, in Chemical Formula 2-11, R is a bond, a C1 to C20 alkylene, ora C2 to C20 alkylene wherein at least one methylene (—CH₂—) is replacedby a sulfonyl group (—S(═O)₂—), a carbonyl group (—C(═O)—), an ethergroup (—O—), a sulfide group (—S—), a sulfoxide group (—S(═O)—), anester group (—C(═O)O—), an amide group (—C(═O)NR—, wherein R is hydrogenor a C1 to C10 linear or branched alkyl group), an imine group (—NR—,wherein R is hydrogen or a C1 to C10 linear or branched alkyl group), ora combination thereof, and

wherein, in Chemical Formula 2-12, R is a C1 to C20 alkylene, or a C1 toC20 alkylene wherein at least one methylene (—CH₂—) is replaced by asulfonyl group (—S(═O)₂—), a carbonyl group (—C(═O)—), an ether group(—O—), a sulfide group (—S—), a sulfoxide group (—S(═O)—), an estergroup (—C(═O)O—), an amide group (—C(═O)NR—, wherein R is hydrogen or aC1 to C10 linear or branched alkyl group), an imine group (—NR—, whereinR is hydrogen or a C1 to C10 linear or branched alkyl group), or acombination thereof,

The polymer layer may not include an unsaturated carboxylic acid, asaturated carboxylic acid, a polymer thereof, or a combination thereof.For example the polymer layer may not include (meth)acrylic acid,benzoic acid, 3-butenoic acid, crotonic acid, butyric acid, isobutyricacid, acetic acid, a polymer thereof, or a combination thereof.

The polymer layer may not include an epoxy moiety or azacyclopropanemoiety. For example, the polymer layer may not include apolyethyleneimine moiety.

The polymer layer may include a monothiol compound including one thiolgroup at the terminal end and/or a multi-thiol compound including atleast two thiol groups. In an embodiment, the monothiol compound mayinclude a C2 to C30 monothiol such as pentanethiol, hexanethiol,heptanethiol, octanethiol, nonanethiol, decanethiol, or dodecanethiol).

The polymer layer may further include a moiety derived from amonounsaturated compound having one carbon-carbon unsaturated bond atthe terminal end (e.g., C3 to C40 monoacrylate compound).

When plurality of nanoparticles including a zinc-containing metal oxideare employed in the electron auxiliary layer of the quantum dot-basedelectroluminescent device, the electron auxiliary layer is expected toshow improved electron transport capability, hole-blocking property, andelectron mobility. In the quantum dot-based electroluminescent device,the emissive layer and the electron auxiliary layer may be prepared by asolution process, so the cost may be saved. However, without being boundby any particular theory, it is believed that the preparation of theelectron auxiliary layer including on the zinc-containing metal oxidefor the quantum dot-based device may be technically challenging since itis difficult to prepare such an electron auxiliary layer having thedesired film qualities and properties.

In an embodiment, the metal oxide nanoparticles have a crystallinestructure. In an embodiment, the metal oxide nanoparticles may beamorphous. The metal oxide nanoparticle in the electron transport layermay be favorable for providing high electron mobility and lowresistance, but which also results in an increased leakage current. Inaddition, it is believed that the oxygen vacancy defect present on ZnOsurface may also be a factor causing the deterioration in performance. Apacking density of the QDs in the emissive layer and the metal oxidenanoparticles in the electron auxiliary layer (for example, each ofwhich are spherical shape particles) may be important. However, aquantum dot-based emissive layer and an electron auxiliary layer basedon zinc-containing metal oxide nanoparticles are vulnerable to theformation of a plurality of voids and cracks therein that may be easilyformed with a grain boundary due to the agglomeration of the pluralityof nanoparticles (or the quantum dots). The voids and cracks may makethe film morphology irregular, which when combined with a high mobilityof the zinc oxide particles, generates a high level of leakage current,thereby resulting in a deterioration in both luminance and efficiency.

In a cadmium-free QD-light emitting diode (QD-LED), the aforementionedelectron auxiliary layer may cause an increase of the leakage current,which may significantly decrease the efficiency and the life-span of theelectroluminescent device. A ligand that passivates the surface of thecadmium-free quantum dot is bound to the surface by a relatively weakbinding force, and as a result, the ligand tends to be easily detached(eliminated) therefrom by heat and/or a carrier (e.g., a hole injectedfrom the positive electrode). The detachment of the ligand is a factorcontributing to the shortened life-span of the cadmium-free quantumdot-based electroluminescent device. As the blue light emitting quantumdot has a high level of excitation energy, the ligand detachmentproblems caused by holes injected during the device operation may bemore serious in case of the blue light emitting quantum dot.

The above-described problems may prevent the quantum dot-based lightemitting device, particularly one prepared by a solution process, fromutilizing its potential merits associated with the use of quantum dots(e.g., high quantum yield, improved color purity, high stability,spectral tenability, etc.).

The device according to an embodiment has the aforementioned polymerlayer on at least a portion of the surface of the second electrode andat least a portion of the surface of the electron auxiliary layer andmay solve the aforementioned problems.

Without being bound by any particular theory, it is believed that thepolymerization product including a moiety derived from a thiol compoundand an unsaturated compound, and included in the polymer layer, maypenetrate into the electron auxiliary layer and into the emissive layer,thereby filling voids/cracks generated in the preparation of theelectron auxiliary layer and the emissive layer, thereby mitigating thenegative influence of the voids/cracks on the electron transportcapability of the electron auxiliary layer and improving the filmuniformity of the electron auxiliary layer and the quantum dot-includedemissive layer. The ligand detachment from the surface of the quantumdot may also be suppressed and the polymerization product may passivateagain the region where the ligand is detached.

Furthermore, without being bound by any particular theory, it isbelieved that a monomer combination used in the formation of the polymerlayer and/or the polymerization product including a moiety derived fromthe monomer combination and included in the polymer layer mayeffectively fill voids and cracks present in the electron auxiliarylayer, the emissive layer, the surface thereof, or a combination thereofwithout having any substantial influence (e.g., while maintainingcarrier path of electron) on a carrier path of electrons duringformation of the polymer layer (or even during the device operation)and, and thus it is estimated that the light emitting device accordingto an embodiment may have a prolonged life-span, enhanced luminousefficiency, and enhanced luminance.

Without being bound by any particular theory, it is believed that thepolymerization product included in the polymer layer and/or anyunreacted monomer (e.g., multiple thiol compound, unsaturated compound,etc.) may penetrate/diffuse into emissive layer during the forming ofthe polymer layer, or even during the device operation. As a result, theregion(s) of the emissive layer where the ligand is detached from thesurface of the quantum dot may be passivated by thiol residues duringdevice operation, so as to enhance the properties of the device(photoluminescence characteristics, stability and life-span).

In an embodiment, the polymer layer may not include an unsaturatedcarboxylic acid, a saturated carboxylic acid compound, a polymerthereof, or a combination thereof. For example, the polymer layer maynot include (meth)acrylic acid or a polymer thereof, benzoic acid,3-butenoic acid, crotonic acid, butyric acid, isobutyric acid, aceticacid, propionic acid, or a combination thereof. According to the presentembodiment, it has been unexpectedly discovered that a carboxylic acidcompound may cause a decrease in the curing degree of the polymer layerand may have a negative influence on device encapsulation.

According to an embodiment, (at least a portion of) the secondelectrode, (at least a portion of) the electron auxiliary layer, andoptionally at least a portion of the emissive layer may be integratedtogether by the polymerization product. Each of the elements (e.g., thecomponents) of the device, according to an embodiment, may be integratedor encapsulated by the polymerization product. In an embodiment, theintegration (e.g., being integrated together) may refer to the casewhere the corresponding components are attached to each other and maynot be separated from one another for example, by application of amanual force.

In an embodiment, the electron auxiliary layer may further includesulfur between the nanoparticles. In an embodiment, the electronauxiliary layer may include an organic material between thenanoparticles, and the organic material may include the polymerizationproduct, unreacted thiol compound, unreacted unsaturated compound, or acombination thereof. The organic material may further include anadditional component included in the monomer combination including thethiol compound and the unsaturated compound, which will be describedlater (e.g., photoinitiator, a moiety included in a curing inhibitor,etc.). The electron auxiliary layer may include a thiol moiety, asulfide moiety, a disulfide moiety, or a combination thereof.

The electron auxiliary layer may include carbon, and the presence of thecarbon may be measured by, for example, an energy dispersivespectroscopy using a transmission electron microscope. In the electronauxiliary layer, a content of carbon may be greater than or equal toabout 1 weight percent (wt %), greater than or equal to about 2 wt %,greater than or equal to about 3 wt %, greater than or equal to about 4wt %, greater than or equal to about 5 wt %, for example, greater thanor equal to about 6 wt %, greater than or equal to about 7 wt %, greaterthan or equal to about 8 wt %, greater than or equal to about 9 wt %,greater than or equal to about 10 wt %, greater than or equal to about11 wt %, greater than or equal to about 12 wt %, greater than or equalto about 13 wt %, greater than or equal to about 14 wt %, greater thanor equal to about 15 wt %, greater than or equal to about 16 wt %,greater than or equal to about 17 wt %, greater than or equal to about18 wt %, greater than or equal to about 19 wt %, or greater than orequal to about 20 wt %, based on the total weight of the electronauxiliary (transport) layer.

In the electron auxiliary layer, a content of carbon may be less than orequal to about 70 wt %, less than or equal to about 65 wt %, less thanor equal to about 60 wt %, less than or equal to about 55 wt %, or lessthan or equal to about 50 wt %, less than or equal to about 45 wt %,less than or equal to about 40 wt %, less than or equal to about 35 wt%, or less than or equal to about 30 wt %, based on the total weight ofthe electron auxiliary layer.

The content of carbon relative to total number of moles of zinc in theelectron auxiliary layer may be measured by energy dispersivespectroscopy of the transmission electron microscope but is not limitedthereto. A content of carbon in the electron auxiliary layer may show aline profile in which the percentage of carbon decreases across thethickness of the electron auxiliary layer toward the emissive layer.

The electron auxiliary layer may include sulfur, and the presence of thesulfur may be measured by an appropriate analysis tool, such as a lineprofile of the energy dispersive spectroscopy of the transmissionelectron microscope.

According to an embodiment, the analysis of the electron microscopeshows that a content of sulfur in the electron auxiliary layer may begreater than or equal to about 0.001 mol %, for example, greater than orequal to about 0.01 mol %, greater than or equal to about 0.05 mol %,greater than or equal to about 0.1 mol %, greater than or equal to about0.5 mol %, or greater than or equal to about 1 mol %, based on the totalnumber of moles of zinc in the electron auxiliary layer. A content ofsulfur in the electron auxiliary layer may be less than or equal toabout 20 mol, less than or equal to about 10 mol %, or less than orequal to about 5 mol %, based on the total number of moles of zinc inthe electron auxiliary layer.

The polymerization product may include a triazine moiety, atriazinetrione moiety, a quinoline moiety, a quinolone moiety, a quinonemoiety, an aryl moiety, an arylphosphine moiety, or a combinationthereof.

The emissive layer may further include an organic material between thequantum dots, and the organic material may include the polymerizationproduct, unreacted thiol compound, unreacted unsaturated compound, or acombination thereof. The organic material may further include anadditional component included in the monomer combination including thethiol compound and the unsaturated compound, which will be describedlater (e.g., photoinitiator, a moiety included in a curing inhibitor,etc.). The electron auxiliary layer may include a thiol moiety, asulfide moiety, a disulfide moiety, or a combination thereof.

In another embodiment, a method of manufacturing the aforementionedlight emitting device includes,

providing a stack structure including:

-   -   a first electrode and a second electrode facing each other,    -   an emissive layer disposed between the first electrode and the        second electrode and including quantum dots, and    -   an electron auxiliary layer disposed between the emissive layer        and the second electrode and including a plurality of        nanoparticles, wherein the plurality of nanoparticles include a        metal oxide including zinc, and the second electrode has a first        surface facing a surface of the electron auxiliary layer and a        second surface opposite to the first surface;

providing a monomer combination (hereinafter, also referred to aspolymer precursor mixture) including a thiol compound (e.g., multiplethiol compound) having at least one (e.g., at least two) thiol (SH)group(s) and an unsaturated compound having at least two carbon-carbonunsaturated bonds;

applying the monomer combination on at least a portion of the secondsurface of the second electrode and on at least a portion of the surfaceof the electron auxiliary layer to form a polymer precursor layer; and

conducting polymerization of the monomer combination (e.g., polymerizing(e.g., cross-linking polymerization) the thiol compound and theunsaturated compound) in the polymer precursor layer to form the lightemitting device.

The method may further include disposing a hole auxiliary layer betweenthe first electrode and the emissive layer.

The first electrode, the second electrode, the emissive layer, theplurality of nanoparticles including the metal oxide including zinc, theelectron auxiliary layer, the hole auxiliary layer, the stack structure,the thiol compound, and the unsaturated compound are the same asdescribed above.

A method of forming the stack structure is not particularly limited andmay be appropriately selected. For example, the aforementioned holeauxiliary layer 12, the emissive layer including quantum dots 13, andthe electron auxiliary layer 14 may be formed with a solution process,for example spin coating, slit coating, inkjet printing, nozzleprinting, spraying, and/or a doctor blade coating, but is not limitedthereto.

The polymer precursor mixture may include the multiple thiol compoundand the unsaturated compound having at least two carbon-carbonunsaturated bonds. A method of forming the monomer combination is notparticularly limited and may be appropriately selected. The monomercombination may be formed by combining the aforementioned multiple thiolcompound and the unsaturated compound in an appropriate manner. In themonomer combination, a ratio of the aforementioned multiple thiolcompound to the unsaturated compound is not particularly limited and maybe appropriately selected. For example, the ratio of the multiple thiolcompound to the unsaturated compound (a ratio between a thiol group anda carbon-carbon double bond) may be greater than or equal to about1:0.1, for example, greater than or equal to about 1:0.2, greater thanor equal to about 1:0.3, greater than or equal to about 1:0.4, greaterthan or equal to about 1:0.5, greater than or equal to about 1:0.6,greater than or equal to about 1:0.7, greater than or equal to about1:0.8, greater than or equal to about 1:0.9, greater than or equal toabout 1:1, greater than or equal to about 1:2 and less than or equal toabout 1:10, for example, less than or equal to about 1:9, less than orequal to about 1:8, less than or equal to about 1:7, less than or equalto about 1:6, less than or equal to about 1:5, less than or equal toabout 1:4, less than or equal to about 1:3, less than or equal to about1:2, less than or equal to about 1:1.9, less than or equal to about1:1.8, less than or equal to about 1:1.7, less than or equal to about1:1.6, less than or equal to about 1:1.5, less than or equal to about1:1.4, or less than or equal to about 1:1.3.

The monomer combination may further include an additional component, forexample, an organic solvent, a monothiol compound, a mono-unsaturatedcompound having one carbon-carbon double bond, a curing inhibitor, aphotoinitiator, a thermal initiator, or a combination thereof. Theadditional component may include a triazine moiety, a triazinetrionemoiety, a quinolone moiety, a quinoline moiety, a quinone moiety, or acombination thereof. The amount of the additional component(s) in thepolymer precursor mixture is not particularly limited but may be, forexample, greater than or equal to about 0.001 parts by weight, greaterthan or equal to about 0.01 parts by weight, greater than or equal toabout 0.1 parts by weight, greater than or equal to about 1 part byweight, greater than or equal to about 2 parts by weight, greater thanor equal to about 3 parts by weight, greater than or equal to about 4parts by weight, greater than or equal to about 5 parts by weight,greater than or equal to about 6 parts by weight, greater than or equalto about 7 parts by weight, greater than or equal to about 8 parts byweight, greater than or equal to about 9 parts by weight, greater thanor equal to about 10 parts by weight, greater than or equal to about 11parts by weight, greater than or equal to about 12 parts by weight,greater than or equal to about 13 parts by weight, greater than or equalto about 14 parts by weight, greater than or equal to about 15 parts byweight, greater than or equal to about 16 parts by weight, greater thanor equal to about 17 parts by weight, greater than or equal to about 18parts by weight, greater than or equal to about 19 parts by weight,greater than or equal to about or 20 parts by weight and less than orequal to about 50 parts by weight, less than or equal to about 40 partsby weight, less than or equal to about 30 parts by weight, less than orequal to about 20 parts by weight, less than or equal to about 10 partsby weight, less than or equal to about 9 parts by weight, less than orequal to about 8 parts by weight, less than or equal to about 7 parts byweight, less than or equal to about 6 parts by weight, less than orequal to about 5 parts by weight, less than or equal to about 4 parts byweight, less than or equal to about 3 parts by weight, less than orequal to about 2 parts by weight, less than or equal to about 1 parts byweight, based on 100 parts by weight of the combined weight of themultiple thiol compound and the unsaturated compound.

FIGS. 2A-2D shows a schematic view of a manufacturing method accordingto an embodiment, as the non-limiting example.

Referring to FIGS. 2A-2D, the monomer combination is coated on a surfaceof a second electrode 15 and a surface of the electron auxiliary layer14 to provide a polymer precursor layer (FIG. 2A). In an embodiment,after forming the polymer precursor layer 16 a, the monomer combinationmay penetrate and/or diffuse between the nanoparticles in the electronauxiliary layer 14 (FIGS. 2B, 2C, and 2D). The penetration and diffusionmay be performed according to an appropriate method. For example, thepenetration and/or diffusion may be performed by gravity and capillaryforce among nanoparticles. The penetration and diffusion may beperformed in an oxygen-free atmosphere.

The method may further include allowing the stack structure on which thepolymer precursor layer is formed to stand for a predetermined timeperiod between the formation of the polymer precursor layer and thepolymerization thereof. In an embodiment, the time period may be greaterthan or equal to about 1 minute, greater than or equal to 2 minutes,greater than or equal to 3 minutes, greater than or equal to 4 minutes,or greater than or equal to 5 minutes and less than or equal to about 1hour, less than or equal to about 30 minutes, or less than or equal toabout 10 minutes. The penetrated and/or diffused material may fill avoid and/or a crack which is present between the metal oxidenanoparticles present in the electron auxiliary layer (e.g., electrontransport layer (ETL)) and/or a void and/or a crack which is presentbetween quantum dots present in the emissive layer. It is described withnon-limiting examples as follows, but it is to help the understandingthe present invention, but not to limit the present invention in anyway.

The monomer combination coated on the surface of the electron auxiliarylayer and on the second surface of the second electrode may fill in avoid which is present among metal oxide nanoparticles of the electronauxiliary layer (e.g., electron transport layer (ETL)) and may bepenetrate through the layer up until the central part of the electronauxiliary layer. According to an embodiment, after forming the polymerprecursor layer including the monomer combination, a substrate (e.g.,cover glass) is placed on the polymer precursor layer to cover thepolymer precursor layer, and subsequently pressed to spread the polymerprecursor mixture across the surface of the electrode and the surface ofthe electron auxiliary layer. Once the monomer combination, or thepolymerization product obtained therefrom, has penetrated/diffusedthrough the thickness of the electron auxiliary layer, it thenpenetrates and diffuses into the emissive layer including the QD, whereit may fill a void and/or crack present among the quantum dots. Themonomer combination which has penetrated into the device may be(radical) polymerized (e.g., along with a lapse of time) and may be, forexample, photopolymerized by irradiating the device with ultravioletlight. For example, the device may be irradiated onto the surface whichis opposite to the surface including with the polymer precursor layer.

As described above, it is believed that the monomer combination (e.g.,thiol compound), which has penetrated the electron auxiliary layer, mayblock the leakage current of the device by removing a defect on thesurface of the Zn-containing oxide nanoparticles and may help to adjustthe electron transport properties of the electron auxiliary layer and toblock hole transfer depending upon a type of the thiol compound and theunsaturated compound (e.g., main moiety of the compounds) in the monomercombination.

In non-limiting examples, it is believed that compounds having thepredetermined moiety, such as1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, etc. block holesduring the operation of the device to improve a possibility to recombinean electron and a hole in the light emitting layer (EML).

When an organic ligand is present on the surface of a quantum dot, thepenetration of the monomer combination may be limited, compared to theelectron auxiliary layer including metal oxide nanoparticles. Butconsidering the morphology of a quantum dot, it is believed that thereare voids into which the monomer combination including the thiolcompound and the unsaturated compound are able to penetrate. In thiscase, it is believed that when the polymer precursor mixture (e.g.,thiol compound) is in contact with the surface of a quantum dot, it maysuppress/prevent the ligand detachment which occurs during the deviceoperation and may form a strong bond in the region where ligand isdetached. The thiol moiety forming a covalent bond with the surface ofthe quantum dot may secure the stability of the quantum dot withoutdetachment during device operation, and thus may enhance the life-span,luminous efficiency, and luminance of the light emitting device.

After or during the penetration and/or the diffusion of the monomercombination, the polymerization of the monomer combination (e.g., thiolcompound and unsaturated compound having at least two carbon-carbonunsaturated bonds) may be performed. The polymerization of the monomercombination may be performed in an oxygen-free atmosphere. The polymerprecursor mixture may further include a photoinitiator and thepolymerization may include photopolymerization. The polymerization maybe performed at a temperature of greater than or equal to about 30° C.,for example, greater than or equal to about 40° C., or greater than orequal to about 50° C. and less than or equal to about 100° C., forexample, less than or equal to about 90° C., or less than or equal toabout 80° C.

A polymerization time may be greater than or equal to about 1 minute,for example, greater than or equal to about 5 minutes, greater than orequal to about 10 minutes, or greater than or equal to about 20 minutesand less than about 4 hours, for example, less than or equal to about 3hours, less than or equal to about 2 hours, less than or equal to about1 hour, less than or equal to about 50 minutes, less than or equal toabout 30 minutes. The penetration/diffusion may be performed atemperature of at less than or equal to about 30° C. or, for example, atroom temperature, and the penetration/diffusion time may be greater thanor equal to about 10 minutes, for example, greater than or equal toabout 20 minutes, greater than or equal to about 30 minutes, greaterthan or equal to about 40 minutes, greater than or equal to about 50minutes and less than or equal to about 10 hours, for example, less thanor equal to about 9 hours, less than or equal to about 8 hours, lessthan or equal to about 7 hours, less than or equal to about 6 hours,less than or equal to about 5 hours, or less than or equal to about 4hours.

The aforementioned light emitting device may be applied to variouselectronic devices such as a display device or a light emitting device.

Hereinafter, the embodiments are illustrated in more detail withreference to examples. However, these examples are exemplary, and thepresent scope is not limited thereto.

EXAMPLES Synthesis of Quantum Dots Reference Example 1: Preparation ofBlue Light Emitting Quantum Dots

(1) Selenium (Se) and tellurium (Te) are respectively dispersed intrioctylphosphine (TOP) to obtain a 2 molar (M) Se/TOP stock solutionand 0.1 M Te/TOP stock solution. 0.125 mmole of zinc acetate is addedalong with oleic acid and hexadecylamine to a reactor includingtrioctylamine and the resulting solution is heated under vacuum at 120°C. After one hour, an atmosphere in the reactor is converted intonitrogen.

Subsequently, the reactor is heated up to 300° C., the prepared Se/TOPstock solution and Te/TOP stock solution are rapidly injected thereintoin a Te:Se ratio of 1:25. After 60 minutes, acetone is added to thereaction solution, is rapidly cooled to room temperature, and aprecipitate obtained after centrifugation is dispersed in toluene toobtain a ZnTeSe core.

(2) 1.8 millimole (mmole) (0.336 g) of zinc acetate is added along witholeic acid to a reaction flask including trioctylamine and thenvacuum-treated at 120° C. for 10 minutes. The atmosphere in the flask issubstituted with nitrogen (N₂) and a temperature is increased up to 180°C. The ZnTeSe core obtained above is added thereto, Se/TOP stocksolution is added and then a temperature is increased up to 280° C.Then, 1M of STOP stock solution is added, a temperature is increased upto 320° C., the Se/TOP stock solution and S/TOP stock solution are addedin predetermined amounts. After the reaction is complete, the reactor iscooled, the prepared nanocrystal is centrifuged with ethanol and isdispersed in toluene to obtain a toluene dispersion of ZnTeSe/ZnSeScore/shell quantum dots.

The used amounts of the S precursor and the Se precursor are about 0.25moles and 0.6 moles pre one mole of the zinc precursor, respectively.

Synthesis of Metal Oxide Nanoparticles Reference Example 2: Synthesis ofZn_(x)Mg_(1-x)O Nanoparticles

Zinc acetate dihydrate and magnesium acetate tetrahydrate are added intoa reactor including dimethylsulfoxide to provide a mole ratio shown inthe following chemical formula and heated at 60° C. in an airatmosphere. Subsequently, an ethanol solution of tetramethylammoniumhydroxide pentahydrate is added into the reactor in a dropwise fashionat a speed of 3 milliliters (mL) per minute (mL/min). After stirring thesame, the obtained Zn_(x)Mg_(1-x)O nanoparticles are centrifuged anddispersed in ethanol to provide an ethanol dispersion of Zn_(x)Mg_(1-x)O(x=0.85) nanoparticles.

The obtained nanoparticles are subjected to an X-ray diffractionanalysis, so it is confirmed that they include a crystalline structure.The obtained nanoparticles are analyzed by a transmission electronmicroscopic analysis, and the results show that the particles have anaverage size of about 3 nm.

The obtained nanoparticles are measured for their UV-Vis absorptionspectrum by using UV-Vis Spectrophotometer (UV-2600, SHIMADZU), and anenergy bandgap of the nanoparticles are obtained from the band edgetangent line of the UV-Vis absorption spectrum. The results show thatthe synthesized nanoparticles have an energy bandgap of about 3.52 eV toabout 3.70 eV.

Reference Example 3: Synthesis of ZnO

ZnO nanoparticles are prepared in accordance with the same procedure asin Reference Example 2, except that the magnesium acetate tetrahydrateis not used.

The obtained nanoparticles are performed with an X-ray diffractionanalysis, so it is confirmed that ZnO crystal is formed. The obtainednanoparticles are performed with the transmission electron microscopicanalysis, and the results show that the particles have an average sizeof about 3 nm.

Manufacture of Light Emitting Device

Unless otherwise noted, the following manufacturing process is performedunder oxygen-free atmosphere.

Comparative Example 1

A glass substrate deposited with indium tin oxide (ITO) is surfacetreated with UV-ozone for 15 minutes, and then spin-coated with aPEDOT:PSS solution (H. C. Starks) and heated at 150° C. for 10 minutesunder air atmosphere and heated again at 150° C. for 10 minutes under N₂atmosphere to provide a hole injection layer (HIL) having a thickness of30 nm. Subsequently,poly[(9,9-dioctylfluorenyl-2,7-diyl-co(4,4′-(N-4-butylphenyl)diphenylamine]solution (TFB) (Sumitomo) is spin-coated on the hole injection layer andheated at 150° C. for 30 minutes to provide a hole transport layer (HTL)having a thickness of 25 nm.

The toluene dispersion of the core/shell quantum dots obtained fromReference Example 1 is spin-coated on the obtained hole transport layerand a heat treatment at 80° C. for 30 minutes is performed to provide anemissive layer having a thickness of 25 nm.

A dispersion (dispersant:ethanol, optical density: 0.5 a.u) ofZn_(x)Mg_(1-x)O (x=0.85) nanoparticles obtained from Reference Example 2is prepared. The prepared dispersion is spin-coated on the emissivelayer and a heat treatment at 80° C. for 30 minutes is performed toprovide an electron auxiliary layer (specifically, electrontransportation layer (ETL)) having a thickness of about 60 nm. Aluminum(Al) is vacuum-deposited on a portion of the surface of the obtainedelectron auxiliary layer in a thickness of 90 nm to provide a secondelectrode, so as to provide a light emitting device shown in FIG. 1.

The obtained light emitting device is evaluated for anelectro-luminescence property using a Keithley 2200 source measurementequipment and a Minolta CS2000 spectroradiometer(current-voltage-luminance measurement equipment). The current,luminance, and electroluminescence (EL) depending upon a voltage appliedto the device is measured by the current-voltage-luminance measurementequipment, and thereby an external quantum efficiency is alsocalculated.

The results are summarized and shown in Table 1, FIGS. 3A, 4A, and 5A.

Example 1

First, a quantum dot light emitting device shown in FIG. 1 ismanufactured in accordance with the same procedure as in ComparativeExample 1.

Then, 0.1 g of a monomer mixture including an unsaturated monomer having2 acrylate groups and an alicyclic main moiety and a multiple thiolcompound represented by the following chemical formula, at a mole ratioof 22:78, is prepared.

Nest, the prepared monomer mixture is coated on the aluminum electrodeand the electron transport layer (ETL) surface (specifically, thesurface of the aluminum electrode and the portion other than the portioncovered by the aluminum electrode of the surface of the electrontransport layer) of the obtained device to provide a polymer precursorlayer. In 5 minutes, a cover glass is disposed on the polymer precursorlayer and pressed, and then the monomer mixture is polymerized at anelevated temperature of about 50° C. by irradiating UV light for about 5minutes under a state in which the device formed with the polymerprecursor layer is heated by irradiating UV light (wavelength: 365 nm,intensity: 600 millijoule per square centimeter (mJ/cm²)) to provide alight emitting device formed with a polymer layer (A+T resin).

The obtained light emitting device is evaluated for electroluminescentproperties using a Keithley 2200 source measurement equipment and aMinolta CS2000 spectroradiometer (current-voltage-luminance measurementequipment). The current, luminance, electroluminescence (EL) dependingupon a voltage applied to the device are measured by thecurrent-voltage-luminance measurement, and thereby an external quantumefficiency is also calculated.

The results are summarized and shown in Table 1, FIGS. 3A, 4A, and 5A.

A cross-section of a surface sample of the obtained light emittingdevice is obtained and a transmission electron microscopic analysis isperformed, and the results are shown in FIG. 7.

Example 2

A light emitting device formed with a polymer layer (TE resin) ismanufactured in accordance with the same procedure as in Example 1,except that 1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (TTT)is used instead of the unsaturated monomer.

The obtained light emitting device is evaluated for electroluminescenceproperties using a Keithley 2200 source measurement equipment andMinolta CS2000 spectroradiometer (current-voltage-luminance measurementequipment). The current, luminance, and electroluminescence (EL)depending upon a voltage applied to the device are measured by thecurrent-voltage-luminance measurement equipment, and thereby theexternal quantum efficiency is also calculated.

The results are summarized and shown in Table 1, FIGS. 3A, 4A, and 5A.

Comparative Example 2

A quantum dot light emitting device is obtained in accordance with thesame procedure as in Comparative Example 1, except that the ZnOnanoparticles obtained from Reference Example 3 are used as the metaloxide nanoparticles.

The obtained light emitting device is evaluated for electroluminescenceproperties using a Keithley 2200 source measurement equipment and aMinolta CS2000 spectroradiometer (current-voltage-luminance measurementequipment). The current, luminance, and electroluminescence (EL)depending upon a voltage applied to the device are measured using thecurrent-voltage-luminance measurement equipment, thereby an externalquantum efficiency is also calculated.

The results are summarized and shown in Table 1, FIGS. 3B, 4B, and 5B.

Example 3

A quantum dot light emitting device formed with a polymer layer (A+Tresin) is obtained in accordance with the same procedure as in Example1, except that the light emitting device which is the same as inComparative Example 2 is used instead of the light emitting devicemanufactured in accordance with the same procedure as in ComparativeExample 1.

The obtained light emitting device is evaluated for electroluminescenceproperties using a Keithley 2200 source measurement equipment and aMinolta CS2000 spectroradiometer (current-voltage-luminance measurementequipment). The current, luminance, and electroluminescence (EL)depending upon a voltage applied to the device are measured using thecurrent-voltage-luminance measurement equipment, thereby an externalquantum efficiency is also calculated.

The results are summarized and shown in Table 1, FIGS. 3B, 4B, and 5B.

Example 4

A light emitting device formed with a polymer layer (TE resin) isobtained in accordance with the same procedure as in Example 2, exceptthat a light emitting device which is the same used as in ComparativeExample 2 is used instead of the light emitting device manufactured inaccordance with the same procedure as in Comparative Example 1.

The obtained light emitting device is evaluated for electroluminescenceproperties using a Keithley 2200 source measurement equipment and aMinolta CS2000 spectroradiometer (current-voltage-luminance measurementequipment). The current, luminance, and electro-luminescence (EL)depending upon a voltage applied to the device are measured using thecurrent-voltage-luminance measurement equipment, thereby an externalquantum efficiency is also calculated.

The results are summarized and shown in Table 1, FIGS. 3B, 4B, and 5B.

Comparative Example 3

A quantum dot light emitting device formed with a polymer layer isobtained in accordance with the same procedure as in Example 1, exceptthat an acrylic resin (acrylate-acrylic acid copolymer, manufacturer:SDI trade name: 1004S) is used instead of the monomer mixture.

The obtained light emitting device is evaluated for electroluminescenceproperties using a Keithley 2200 source measurement equipment and aMinolta CS2000 spectroradiometer (current-voltage-luminance measurementequipment). The current, luminance, and electroluminescence (EL)depending upon a voltage applied to the device are measured using thecurrent-voltage-luminance measurement equipment, thereby an externalquantum efficiency is also calculated.

The results are summarized and shown in Table 1, FIGS. 3A, 4A, and 5A.

TABLE 1 Max. Lamda FWHM Max T 50 Description EQE_(max) Cd/A max. (nm)Lum (h) Comp. Blue QD/ZnMgO 4.3 2.5 454 26 4960 0.4 Ex. 1 Ex. 1 BlueQD/ZnMgO/A + T 9.0 5.7 455 26 17720 8.8 Ex. 2 Blue QD/ZnMgO/TE 8.8 5.7455 26 15990 7.6 Comp. Blue QD/ZnO 2.7 1.6 455 26 2080 0.2 Ex. 2 Ex. 3Blue QD/ZnO/A + T 3.2 1.9 455 26 4140 16.5 Ex. 4 Blue QD/ZnO/TE 7.8 4.5455 26 4480 7.0 Comp. Blue 6.6 3.7 454 26 4940 1.1 Ex. 3QD/ZnMgO/Acrylic * EQE_(max): maximum external quantum efficiency * MaxCd/A: maximum current efficiency * T 50 (h): on driving at 100 nit, time(hr) for gaining the luminance of 50% with respect to 100% ofluminance * Lambda max and FWHM: EL peak wavelength and full width athalf maximum (FWHM) * Max Lum: maximum luminance * ZnMgO:Zn_(x)Mg_(1-x)O (x = 0.85)

From the results, it is confirmed that the light emitting devicesaccording to Examples 1 to 4 have improved electroluminescenceproperties and life-span characteristics comparing to the light emittingdevices according to Comparative Examples.

Experimental Example 1

[1] Cross-sectional surfaces of the light emitting device according toComparative Example 2 and the light emitting device according to Example3 are performed with a transmission electron microscope-energydispersive spectroscopy. The results show that a content of carbonrelative to zinc in the device according to Comparative Example 2 isinsignificant; on the other hand, a content of carbon relative to zinc(43 mol %), which is greater than or equal to 20 mol % in the deviceaccording to Example 3.

[2] TEM-EDX line profile is obtained for a cross-sectional surface ofthe light emitting device according to Example 3. The results show thata content of carbon in the electron auxiliary layer shows a maximumvalue on the surface facing the second electrode with a decreasinggradient moving towards the emissive layer. The TEM-EDX line profile ofthe cross-sectional surface of the light emitting device according toExample 3 shows that surfer is present in the electron auxiliary layer.

Experimental Example 2

The toluene dispersion of the blue light emitting core/shell quantumdots obtained from Reference Example 1 are spin-coated on a glasssubstrate and a heat treatment at 80° C. for 30 minutes is performed toprovide a quantum dot layer having a thickness of 25 nm, and an ethanoldispersion of Zn_(x)Mg_(1-x)O (x=0.85) nanoparticles obtained fromReference Example 2 is spin-coated on the quantum dot layer and a heattreatment at 80° C. for 30 minutes is performed to provide aZn_(x)Mg_(1-x)O layer, so as to obtain a Ref stack structure. A polymerlayer is formed on the Zn_(x)Mg_(1-x)O layer of the Ref stack structureusing the monomer combination according to Example 2 by irradiating UVlight (wavelength: 365 nm, intensity: 600 mJ/cm²) for 20 seconds, so asto prepare a stack structure having a quantum dot layer-Zn_(x)Mg_(1-x)Onanoparticle layer-polymer layer.

The Ref stack structure and the stack structure are irradiated withlight having a wavelength of 365 nm and a photoluminescence analysis isperformed, and the results are shown in FIG. 6.

From the results of FIG. 6, it is confirmed that the stack structurehaving the polymer layer may show greatly improved luminescenceproperties compared to the Ref stack structure, especially greatlyincreased luminescence intensity at the peak emission wavelength.

While this disclosure has been described in connection with what ispresently considered to be practical example embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A method of manufacturing a light emittingdevice, the method comprising: providing a stack structure comprising afirst electrode and a second electrode facing each other, an emissivelayer disposed between the first electrode and the second electrode andcomprising a quantum dot, and an electron auxiliary layer disposedbetween the emissive layer and the second electrode, providing a polymerprecursor mixture comprising a thiol compound having at least one thiolgroup and an unsaturated compound having at least two carbon-carbonunsaturated bonds; applying the polymer precursor mixture on the secondelectrode and on the electron auxiliary layer to form a polymerprecursor layer; and polymerizing the thiol compound and the unsaturatedcompound in the polymer precursor layer to form the light emittingdevice.
 2. The method of claim 1, wherein the electron auxiliary layercomprises a plurality of nanoparticles.
 3. The method of claim 2,wherein the plurality of nanoparticles comprises a metal oxide having acomposition represented by Zn_(1-x)M_(x)O (wherein, M is Mg, Ca, Zr, W,Li, Ti or a combination thereof and 0≤x≤0.5).
 4. The method of claim 1,wherein the second electrode has a first surface facing a surface of theelectron auxiliary layer and a second surface opposite to the firstsurface, and wherein the polymer precursor mixture is applied on atleast a portion of the second surface of the second electrode and on atleast a portion of the surface of the electron auxiliary layer.
 5. Themethod of claim 1, wherein the quantum dot comprises a Group III-Vcompound comprising indium and phosphorous, a Group II-VI compoundcomprising zinc and a chalgen, or a combination thereof.
 6. The methodof claim 1, wherein the quantum dot does not comprise cadmium.
 7. Themethod of claim 1, wherein the polymer precursor mixture furthercomprises a photo initiator.
 8. The method of claim 1, wherein thepolymer precursor mixture does not comprises a (meth)acrylic acid,benzoic acid, 3-butenoic acid, crotonic acid, butyric acid, isobutyricacid, acetic acid, propionic acid, or a combination thereof.
 9. Themethod of claim 1, wherein the polymerizing of the polymer precursorlayer comprises photopolymerization.
 10. The method of claim 9, whereinthe photopolymerization comprises irradiating the polymer precursorlayer with UV light.
 11. The method of claim 1, wherein the polymerizingof the polymer precursor layer is performed at a temperature of greaterthan or equal to about 30° C.
 12. The method of claim 1, wherein thepolymerizing is performed in an atmosphere without oxygen.
 13. Themethod of claim 2, wherein the polymer precursor mixture penetrates anddiffuses between nanoparticles of the plurality of nanoparticles in theelectron auxiliary layer before the polymerizing, during thepolymerizing, or a combination thereof.
 14. The method of claim 1,further comprising allowing the stack structure on which the polymerprecursor layer is formed to stand for at least 1 minute between theforming of the polymer precursor layer on the stack structure and thepolymerizing of the thiol compound and the unsaturated compound in thepolymer precursor layer.
 15. A method of manufacturing a light emittingdevice, the method comprising: providing a stack structure comprising afirst electrode and a second electrode facing each other, an emissivelayer disposed between the first electrode and the second electrode andcomprising a quantum dot, and an electron auxiliary layer disposedbetween the emissive layer and the second electrode, providing a polymerprecursor mixture comprising a thiol compound having at least one thiolgroup, an unsaturated compound having at least two carbon-carbonunsaturated bonds, and a photoinitiator; applying the polymer precursormixture on the stacked structure to form a polymer precursor layer;irradiating the polymer precursor layer with UV light, and polymerizingthe thiol compound and the unsaturated compound in the polymer precursorlayer to form the light emitting device.
 16. The method of claim 15,wherein the electron auxiliary layer comprises a plurality ofnanoparticles.
 17. The method of claim 16, wherein the plurality ofnanoparticles comprises a metal oxide having a composition representedby Zn_(1-x)M_(x)O (wherein, M is Mg, Ca, Zr, W, Li, Ti or a combinationthereof and 0≤x≤0.5).
 18. The method of claim 15, wherein the secondelectrode has a first surface facing a surface of the electron auxiliarylayer and a second surface opposite to the first surface, and whereinthe polymer precursor mixture is applied on at least a portion of thesecond surface of the second electrode or on at least a portion of thesurface of the electron auxiliary layer.
 19. The method of claim 15,wherein the polymer precursor mixture does not comprises a (meth)acrylicacid, benzoic acid, 3-butenoic acid, crotonic acid, butyric acid,isobutyric acid, acetic acid, propionic acid, or a combination thereof.20. The method of claim 15, wherein the polymerizing of the polymerprecursor layer comprises photopolymerization.